What in-world explanation do you use for "adventuring party sizes"?

[47948201]

I've been thinking about the standard D&D party being 4-6 people lately. It makes sense for real-life logistical reasons--it's hard to get 10, 15, or 20 people together for a scheduled game, and even harder then to give each of those players a chance to shine when only one DM is managing everyone.

But in-world, in a classic D&D setting where "adventurers" are common enough that you can reliably head to your local tavern to tell the newest group about the goblins nearby, why wouldn't an adventuring party want to have more people? Sure, you'll consume more resources and split treasure more ways, but isn't that worth the greatly increased chances of survival, or the faster dungeon clear rate in any case? I guess a large party also makes stealth difficult, but that feels more like a "roguish party's concerns" rather than something that would really become conventional across your entire generic medieval fantasy world. If you happen to only have 3 adventure-worthy friends, then make a mini-party and meet a couple more groups of 3-4 people to team up with. Call it an alliance, or perhaps a company, or maybe even... I dunno, a fellowship?

Unless, that is, there's some kind of in-universe explanation that adventurers rarely (or never) form groups of more than 4-6. If you've got one or more you like to use, then would you mind sharing with the class?

[Satinavian]

Easy answer :

Bigger groups do exist. They are generally called "bands", "mercenary companies" or "armies". But the big groups are not a good fit for every task which is why the smaller ones still exist. Also with more people tend to come hierarchy and formalized rules which is not for every one. The individualists stick to small groups.

[Mechalich]

Easy answer :

Bigger groups do exist. They are generally called "bands", "mercenary companies" or "armies". But the big groups are not a good fit for every task which is why the smaller ones still exist. Also with more people tend to come hierarchy and formalized rules which is not for every one. The individualists stick to small groups.

Right, and an adventuring party can be thought of as the smallest operational unit of any military force. 4-6 people is actually a perfectly reasonable match for real-world military units, and a plausible match for a medieval unit with the exception of the equality of rank: a medieval knight, just out in the countryside, would have multiple associates with them. Amusingly the 2001 film A Knight's Tale, though a spoof, represents this quite well, as Heath Ledger's 'knight' travels from one tournament to another accompanied by two squires, a herald, and an armorer.

[Vahnavoi]

"Adventurer" is a wastebin category that includes any kind of vagrant worker from thieves and mercenaries to merchants and pilgrims.

An "adventuring party" is hence a wastebin category that contains any small group coming together for any of those various reasons.

It isn't actually hard to figure out why only limited amount of people would partake in an endeavor. Many of the reasons are the same logistical limitations that keep you from having arbitrarily many players.

In any case, larger groups do exist and have their own terms - terms for military units being an example already given. Indeed, quite often an "adventuring party" is just a small military unit that is part of a larger organization, namely a squad. Add in retainers and other back-up characters, and the true size of the "party" can in fact be a section or a platoon.

[Batcathat]

In addition to the suggestions that's already been made, it could also be a legal issue (at least in more civilized parts of the setting). Add enough people and it's starting to look less "adventure party" and more "private army", which the people in charge might have an issue with.

[Mastikator]

Adventuring groups are few and far in between, they tend to consist of 3-6 heroes. Adventuring parties only arise during interesting times, not something you can expect to find roaming around. Adventuring parties are a unique and special thing.

Explorers, cartographers, prospectors and the like are not adventuring parties, they proceed carefully, if they encounter trolls they flee or they die. Any region that is overgrown with monsters and can not be traversed by NPC class humanoids are uncharted- "here be dragons".
Likewise for warriors, mercenaries are not explorers, armies do not exist for exploration or adventure. The the only thing that does both exploration and combat is conquering armies, but they don't do quests, they raid, take over and establish a new order.

[Mr Blobby]

Yes; the 'fireteam' is normally between 4-6 persons. Part of the argument for this is allows the team to have a mix of skills/firepower to be actually useful without having to have reliant on hugely overly-skilled members. In militaries, I also supect the 'max team numbers' will be the same as the max capacity of their standard light recon/transport vehicle.

Now into D&D [or any adventuring game, really].

First off, fighting in 'dungeons' normally neutralises numerical superiority - logjams happen and the rear persons cannot really do anything without hurting the friendlies in front of them. It's also stuffed with pinch-points, in which in games shall often be the bit where our magic-users will lob ranged spells at and rogues will lace with traps. Sending a whole platoon [unless a large dungeon with muti entries etc] would be a waste of resources.

Next, obviousness. When a band of 50 'people' move through an area, folks will notice; even in relative wilderness. If you're the Bad Folks, you will instantly know they're Coming For Us and prepare. However, a team of four/five/six are both less likely to be noticed and could be mistaken for something else.

Third, logistics. In pseudo-medieval settings [like D&D], most inns etc are not geared to be able to cater to 25+ people [plus horses etc], which means they'll have to [normally] travel with their baggage train, which is slow as hell. A small team, however should be able to 'live off the land' [ie use civilian resources etc] so they can travel light [and thus, move faster].

Lastly, capability. Many of the 'adventures' are too much for one/two rookies to handle [which is why the quest-givers haven't done it themselves] but don't require a whole platoon to achieve. The 'team' in this case is skilled/flexible enough to handle a lot of problems on their own [and perhaps skilled enough to know what they can't handle and retreat in good order] but not at a prohibitive cost. There's also nothing stopping a couple of teams to work together on larger missions.

Which is perhaps the point the OP is missing - that the group are the folks who go on adventures, not necessarily as 'for hire' adventurers. A whole chronicle could be built around [for example] a 'special forces' team within an army [most did have these, but didn't call them such] which gets the fun things to do while the footsloggers are stuck with sentry duties, building palisades and now and then being a helmet during a conventional action.

[Unoriginal]

Sure, you'll consume more resources and split treasure more ways, but isn't that worth the greatly increased chances of survival, or the faster dungeon clear rate in any case?

That is a calculation many people will disagree on, in-universe.

Even assuming that a lot of people can go in a dungeon at the same time without the consequences make it *less* safe (ex: it's easier to infiltrate an half-sunken temple guarded by lizardfolks when you're 4 than when you're 20), not everyone values safety the same way.

In fact in many case people only become adventurers voluntarily when they're the type who don't mind doing something risky so long as there is a big payday at the end.

If you ask that kind of person "yeah but why not do something safer for a small payday?", they'd probably tell you something like "if I wanted safe I'd be growing food somewhere where the army deals with criminals and monsters"

[Mr Blobby]

Choose your future. Choose life... But why would I want to do a thing like that? I chose not to choose life. I chose somethin' else.

Every society produces a % of 'misfits', who don't want the paint-by-numbers 'life' offered. These folks will try to escape it even if staying with 'the instructions' [like farming, or operating a shop] was from a material POV a better choice for them. 'Adventurers' are often these folks; that they want more than to simply find a comfortable groove that they can go around in until death.

[Biggus]

I think one major reason is that 4-5 people is just enough to have all the key specialities covered. The classic party setup of Cleric, Rogue, Wizard and Fighter, with maybe a Bard for good measure. As others have mentioned, this is the minimum unit size in real-world militaries, and for similar reasons.

Adventuring groups are few and far in between, they tend to consist of 3-6 heroes. Adventuring parties only arise during interesting times, not something you can expect to find roaming around. Adventuring parties are a unique and special thing.

This depends on the setting. In some adventurers are, while still not exactly common, a lot less rare than you describe here.

[Tanarii]

They're mercenary magical special forces squads. That's the role they function in. Even if they're not officially incorporated or associated with a larger mercenary band. Unless they're doing it for altruistic reasons, and leaving all the loot behind. Then they're non-mercenary do-gooder magical tactical forces squads or something.

Larger bands are usually just mercenaries or mobs, depending on if they're doing it for loot/reward or revenge/"justice". They usually have fewer 'level-equivalent' or 'class-equivalent’ types because those guys are specialists and drift into the special forces role.

This depends on the setting. In some adventurers are, while still not exactly common, a lot less rare than you describe here.

Given the Thread title (if not the OP) is reasonable to assume any universal statements someone is making are about their setting.

So to be clear, when I say adventuring parties are "mercenary magical special forces squads" that is a universal statement for any setting with magic where adventurers do adventuring things for reward/loot.

[Mr Blobby]

I think one major reason is that 4-5 people is just enough to have all the key specialities covered. The classic party setup of Cleric, Rogue, Wizard and Fighter, with maybe a Bard for good measure. As others have mentioned, this is the minimum unit size in real-world militaries, and for similar reasons...

Which in a modern setting is Medic/Rogue/Brains/Muscle, with 'Face' an optional for groups which need to do a lot of social work. This size also means they can [in a pinch at times] all get into the same car. It is also the bare minimum size where a group can be sub-divided without any person being alone.

[Grod_The_Giant]

IBut in-world, in a classic D&D setting where "adventurers" are common enough that you can reliably head to your local tavern to tell the newest group about the goblins nearby, why wouldn't an adventuring party want to have more people?

Where does it say there are bands of adventurers wandering all over the setting? Even if party-spawning circumstances happen fairly often (unlikely), you have to figure that the vast majority fall apart when half the team dies in the first fight. And the small number who do manage to make it through their first adventure, why would they do it again?

The player characters are exceptional by definition.

[Mastikator]

This depends on the setting. In some adventurers are, while still not exactly common, a lot less rare than you describe here.

Yeah but whenever I see a setting with tons of adventuring parties I start to wonder "how many creatures does the average party kill in their career" and "how many parties are there", it makes me wonder "how can anybody be left".
Like in *Critical Role's setting it seems like you'll find at least a couple of adventuring parties in any given tavern, and it just doesn't seem sustainable? It makes me feel like I'm playing WoW except the NPC adventurers didn't even earn their level. It cheapens it for me.

*correct me if I'm wrong, I have barely seen one episodes worth of CR, but I did watch the Legend of Vox Machina and that part of the show made me cringe a bit.

[Mechalich]

Yeah but whenever I see a setting with tons of adventuring parties I start to wonder "how many creatures does the average party kill in their career" and "how many parties are there", it makes me wonder "how can anybody be left".

There have been, in history, periods of time when adventurer-type people proliferate. Game-designers are actually aware of this and tend to set a lot of games during such periods, which include the 'Wild West' in the United States, Three Kingdoms China, and the early Tokugawa Shogunate period in Japan. The reason for this is simple: the most common genesis of an 'adventurer' is someone who used to be a soldier, but the army they fought for was disbanded and for some reason they are unsuited to go back home to civilian life (for reasons ranging from PTSD to their home being destroyed during the war). If there are lots of people like this, usually because some big war just ended, adventurers proliferate.

But yes, this is time limited. Even though traditionally adventurers have expended a lot of their effort against each other, sending large numbers of heavily armed and trained combatants into some semi-settled or wilderness area is going to transform that area in short order. The 'Wild West' lasted from ~1865 - when the Civil War ended and all the veterans spilled into it - to ~1910 - when the railroads finished linking up even remote regions in the Dakotas and Wyoming and the influence of 'civilization' slammed back. And yes, the presence of all those adventurers reshape the environments they operate within. For example, in the wild west, the populations of large mammals like bison and wolves plummeted.

[wilphe]

The very birth and early years of D&D aren't necessarily about small adventuring groups

You might have 4-6 players, but you go in there with hirelings, war dogs, porters and torchbearers

This is also why doppelgangers exist, as part of the player-GM arms-race to teach you not to bring more underlings than you can keep track of and suss when one has been eaten and replaced


This is much less true of later editions, some would put the transition at 3E, some at 2E

[wilphe]

Yeah but whenever I see a setting with tons of adventuring parties I start to wonder "how many creatures does the average party kill in their career" and "how many parties are there", it makes me wonder "how can anybody be left".

In one of the Fleming Novels it is remarked that Bond might only do one or two missions a year

When adventuring can be so lucrative, groups might spend months between adventures living off their loot and following up rumours to prepare for the next one

Especially if you are in a campaign or edition where you have to train to level up

[Leon]

None, there is no "standard" there is what happens and works

[Sure_Is_Dusty]

The lack of larger adventuring parties could be a case of "too many cooks spoil the soup". The more people you have working together, the more likely to have personality clashes, with differences of opinion on how to handle the group's objectives. In a group of 4, it's much easier to talk a single person down from acting out on their own, but in a group of 10, it's harder to convince 4 of them from leaving if they don't support the rest of the party's plans.

[KorvinStarmast]

What in-world explanation do you use for "adventuring party sizes"?

The rarity of adventurers in the first place. You make some unwarranted assumptions. In world, when I DM, I discuss with each player where they came from (it needs to fit into the world) and we arrive at a plausible explanation for why they ended up "here" where these other 3, 4, 5, or 6. people are. (We've been running a group of 6-8 in my Wednesday group since late 2014, with a few breaks as DM's get hit with real life).

I've been thinking about the standard D&D party being 4-6 people lately.

Watch the movie "The Magnificent Seven" (James Coburn, Steve McQueen, Yul Brynner) and subtract 1. There you go.

But in-world, in a classic D&D setting where "adventurers" are common enough that you can reliably head to your local tavern to tell the newest group about the goblins nearby

There's your first wrong assumption, or rather, presumption. Adventurers are rare in each setting I've played in. There's a reason for that. Most of them die (off screen) someth8ing along the lines of "nobody returns from the Kreepy Forest" ... and indeed the last two bands of explorers/ adventurers didn't return ... or maybe one survivor came back and she's gone mad. She may even be able to explain, in a lucid moment, what they were looking for before she goes off on another rant of gibbering and drooling ... Try that for an adventure hook sometime.

, why wouldn't an adventuring party want to have more people? Sure, you'll consume more resources and split treasure more ways, but isn't that worth the greatly increased chances of survival, or the faster dungeon clear rate in any case?

You are assuming a level of meta game knowledge for your "in world" justification.

I guess a large party also makes stealth difficult

Yes. While there is some security in numbers, the ability to move without attracting too much attention is valuable.

Right, and an adventuring party can be thought of as the smallest operational unit of any military force. 4-6 people

Yes, a Fire Team (+). (Doctrinal squad in the US Army is/was 11 back when I was working force structure projects, doctrinal squad in the USMC was 13; each made of up 3 fire teams and some leadership ... not sure if that's still the case... the USMC fire teams were 4, the Army were 3).

"Adventurer" is a wastebin category

Yes.

Adventuring groups are few and far in between, they tend to consist of 3-6 heroes. Adventuring parties only arise during interesting times, not something you can expect to find roaming around. Adventuring parties are a unique and special thing.

Bingo. With that said, the idea of adventuring guilds does have some parallel to gangs, or to explorers in the 18th and 19th century who ended up exploring a variety of places ... but those expeditions had a lot of logistical support that numbered in the dozens.

Any region that is overgrown with monsters and can not be traversed by NPC class humanoids are uncharted- "here be dragons".

Conan, Valeria, and Subotai were a three person adventuring party/quest party in the Arnold S. Conan movie, with a 4th shaman/wizard who assisted here and there.

Next, obviousness. When a band of 50 'people' move through an area, folks will notice; even in relative wilderness.

Which also may draw people wanting to ambush the party as they return from the ruins with their loot.

We had that happen a few times in our old school games: bandits (who had observed us leaving for the ruins) trying to take our loot after we'd risked our lives for it. Another reason not to advertise what you are on about ...

..most inns etc are not geared to be able to cater to 25+ people ...A small team, however should be able to 'live off the land'

Also a good point.

The 'team' in this case is skilled/flexible enough to handle a lot of problems on their own [and perhaps skilled enough to know what they can't handle and retreat in good order] but not at a prohibitive cost. There's also nothing stopping a couple of teams to work together on larger missions.

See also the 'team' put together for the movie The Guns of Navarrone.

Which is perhaps the point the OP is missing - that the group are the folks who go on adventures, not necessarily as 'for hire' adventurers.

For my Saltmarsh campaign, before the book came out, I got the group started near a wilderness area where a group of religious pilgrims were having a gathering (kind of like a modern day religious retreat, families included) and they ran into trouble.
The adventure hook was a cart coming into town with two people telling a tale of monsters attacking the camp, and of bandits kidnapping children ... the party basically went out looking to recover the lost/kidnapped kids.

If you ask that kind of person "yeah but why not do something safer for a small payday?", they'd probably tell you something like "if I wanted safe I'd be growing food somewhere where the army deals with criminals and monsters"

No boldness, no blue chips. High Risk, High Reward.

They're mercenary magical special forces squads. That's the role they function in.

This also.

Which in a modern setting is Medic/Rogue/Brains/Muscle, with 'Face' an optional for groups

Blades in the Dark does this quite well.

Where does it say there are bands of adventurers wandering all over the setting? .... The player characters are exceptional by definition.

Bingo. Mind you there can be rivals (like Beloch in Raiders of the Lost Arc) who are trying to recover the same treasure ...

The very birth and early years of D&D aren't necessarily about small adventuring groups. You might have 4-6 players, but you go in there with hirelings, war dogs, porters and torchbearers

This is also why doppelgangers exist, as part of the player-GM arms-race to teach you not to bring more underlings than you can keep track of and suss when one has been eaten and replaced

True, and a different style of the same game. (If you go to the Blog of Holding web site, and read up on the adventures the author had with Mike Mornard as DM, you get a nice feel for how a lot of that works out.

None, there is no "standard" there is what happens and works

This too. See the Conan example above.

[Darth Credence]

I don't. I've never seen any need for such an explanation.

There are large groups that go and clear dungeon and cave systems. There are travelers out to see the world, who learn how to protect themselves while out there. There are people that have experienced tragedies, and so band together with friends to do something about it. There are people seeking power, money, or glory, and band together with friends to get it. As many reasons for adventuring exist as there are adventuring parties, and the size of the given group depends on those reasons.

[Grim Portent]

I've never encountered a good reason in setting to not have a medley of hirelings running around making us more of a mercenary company than an 'adventuring party.' There really isn't much that four people can do better than fifty, and splitting loot doesn't really matter much.

Usually it just boils down to conservation of narrative type meta reasoning. Hirelings don't do active stuff, they carry things or do rearguard stuff while the 'important' people go ahead and handle negotiations, or slay monsters and so on, so you might as well just ignore the sidekicks and the parts of the game they exist to handle.


I'm actually getting to the point where I would happily handle a bloody spreadsheet* of expenses for mercenary wages, supplies and transport just so I actually have something to do with the money I get in game, even if the mercs are just serving as a narrative framing device and a way to carry things without a bag of holding.**


*I did make three such spreadsheets for fun, even bouncing off my brother for what amount of food things like horses, worgs and ogres would need, so I'm a bit odd in this regard.

**I've actually gotten really bored of bag's of holding and other hammerspace type stuff which make carrying things unimportant. I want a couple of wagons to carry my wagonload of things, not a cartoon character's magical pocket that we always get because it's convenient for the DM.

[Gnoman]

Turn the question around. What benefit do larger parties offer? Adventuring parties do much of their work in tight quarters, not open-field battle. If you're advancing down a corridor that barely allows one or two guys room to fight, what benefit does an extra three guys with swords give you? What does extra archers give you when the one bowman you have has trouble picking out targets past allies?

[Mr Blobby]

There have been, in history, periods of time when adventurer-type people proliferate. Game-designers are actually aware of this and tend to set a lot of games during such periods, which include the 'Wild West' in the United States, Three Kingdoms China, and the early Tokugawa Shogunate period in Japan. The reason for this is simple: the most common genesis of an 'adventurer' is someone who used to be a soldier, but the army they fought for was disbanded and for some reason they are unsuited to go back home to civilian life (for reasons ranging from PTSD to their home being destroyed during the war). If there are lots of people like this, usually because some big war just ended, adventurers proliferate.

But yes, this is time limited. Even though traditionally adventurers have expended a lot of their effort against each other, sending large numbers of heavily armed and trained combatants into some semi-settled or wilderness area is going to transform that area in short order. The 'Wild West' lasted from ~1865 - when the Civil War ended and all the veterans spilled into it - to ~1910 - when the railroads finished linking up even remote regions in the Dakotas and Wyoming and the influence of 'civilization' slammed back. And yes, the presence of all those adventurers reshape the environments they operate within. For example, in the wild west, the populations of large mammals like bison and wolves plummeted.

I think this can be put even easier; where/when you find locations with relative power-vacuum, you will find 'adventurers', doing much of the tasks in more 'normal times' would be done by organised authorities [or perhaps stopped by them] and/or taking advantage of the vacuum to try their hand at things which is normally much harder/impossible to do.

I've never encountered a good reason in setting to not have a medley of hirelings running around making us more of a mercenary company than an 'adventuring party.' There really isn't much that four people can do better than fifty, and splitting loot doesn't really matter much.

Usually it just boils down to conservation of narrative type meta reasoning. Hirelings don't do active stuff, they carry things or do rearguard stuff while the 'important' people go ahead and handle negotiations, or slay monsters and so on, so you might as well just ignore the sidekicks and the parts of the game they exist to handle.


I'm actually getting to the point where I would happily handle a bloody spreadsheet* of expenses for mercenary wages, supplies and transport just so I actually have something to do with the money I get in game, even if the mercs are just serving as a narrative framing device and a way to carry things without a bag of holding.**

I actually think this is the way it should go for long-running chronicles with high-level PCs. That once you're starting to touch let's say, L-15 you're entering 'demigod' territory re: normal threats, your mere existence has a gravitational pull of it's own [NPCs will notice you and as a 'major player' somebody will always have tabs on your movements etc] and like it or not, it's likely you have some form of 'responsibility' which means you can't go and 'dash off and have an adventure' like you did when young. But then you remember that unlike those 'good old days', you now have minions/ retainers/ apprentices/ hirelings who can do a lot of the dull slog [loot collection/disposal, sorting out supplies, setting up base camps, gathering basic intel etc] which is good because part of your concerns now are at least national in scope, perhaps starting to involve other Planes so dealing with a load of bandits etc is simply an inconvenience.

Plus, by this time you've normally met loads of NPCs, some of which you've turned into retainers/allies.

[Biggus]

Given the Thread title (if not the OP) is reasonable to assume any universal statements someone is making are about their setting.

In the OP it says

in a classic D&D setting where "adventurers" are common enough that you can reliably head to your local tavern to tell the newest group about the goblins nearby

So my understanding of what they mean is "in worlds where adventurers are rare, it'd be hard enough to find even two or three other people to adventure with, so it makes sense that large parties would be very rare; but why are they rare in settings where adventurers are common?".

Yeah but whenever I see a setting with tons of adventuring parties I start to wonder "how many creatures does the average party kill in their career" and "how many parties are there", it makes me wonder "how can anybody be left".
Like in *Critical Role's setting it seems like you'll find at least a couple of adventuring parties in any given tavern, and it just doesn't seem sustainable? It makes me feel like I'm playing WoW except the NPC adventurers didn't even earn their level. It cheapens it for me.

You're jumping from one extreme to the other here. What I said was

In some adventurers are, while still not exactly common, a lot less rare than you describe here

There's a very large middle ground between "few and far in between...a unique and special thing" and "at least a couple in any given tavern".

In most games I've played in, high-level adventurers are rare and special, low-level ones are uncommon but not super-rare. After all, by mid-levels you've made enough money to settle down very comfortably for the rest of your life; many of those who don't get killed early on will likely do this ("tavern owned by a former adventurer" is a pretty common FRPG trope). Those who make it to high levels and neither die or retire will be rare in nearly all settings.

In one of the Fleming Novels it is remarked that Bond might only do one or two missions a year

When adventuring can be so lucrative, groups might spend months between adventures living off their loot and following up rumours to prepare for the next one

This is certainly how it is when I DM. Apart from anything else, having your magic items upgraded can take weeks or months at high levels (or at epic levels potentially even years) and finding someone willing to sell you a rare magic item can take a long time, so just spending the loot from your last adventure can require a lot of downtime.

[Tanarii]

In the OP it says

Yes. But the thread title implies that it invites folks to post based on their own setting. I think it would have been better if I'd just written: Agreed, but posting based on the title without reading the OP is a time honored tradition.

[Luccan]

Worth pointing out pretty much every version of D&D at least mentions the idea of hiring more help, so 20-50+ people systematically clearing a dungeon is absolutely a way you can play. You just don't need that many players to do so.

But I think regardless of edition if you want to justify the small party sizes just think about what adventuring actually entails. it's extraordinarily dangerous to adventure so the selection pool is small. Possibly so small as to make the 4-6 heroes in this party the only adventurers. Either that any of the PCs know or simply the only adventurers depending on your feeling on having other adventuring parties exist in your games. But in addition to the obvious dangers, the circle of people you can trust might be small in a high-risk, high-reward game like adventuring. Even if you only assume you'll have to deal with illusions and other trickery in the dungeon, you don't want to have to bet your life on if you can tell a Guy You Never Talk To from a Doppelganger Wearing His Face

[Jay R]

Peter, Susan, Edmund, Lucy.
Athos, Porthos, Aramis, D'Artagnan.
Luke, Obi-Wan, Han, Chewbacca, R2-D2, C-3PO.
Fred, Velma, Daphne, Shaggy, Scooby.
Reed, Sue, Ben, Johnny.
Yakko, Wakko, Dot.
Harry, Ron, Hermione.
Dorothy, Toto, Scarecrow, Tin Woodman, Lion.
Larry, Curly, Moe.
Captain America, Iron Man, Black Widow, Thor, Hawkeye, Hulk.
Inigo, Fezzik, Vizzini.
Sheldon, Leonard, Rajesh, Howard.
Peter, Gamora, Drax, Rocket, Groot.

Star Trek captains have hundreds of crew, and the away team is always four to six.

I'm not sure why I would need to explain it.

[Kardwill]

I don't. I've never seen any need for such an explanation.

I'm in the same boat. The "4-6 member adventuring party" is not really a thing that exists in my universe. My player's party happens to be a group of 4-6 adventurers, sure, but that doesn't mean there are others like it. There are groups of tomb raiders, or explorers, or mercenaries, or errant knights, or thugs, that call themselves adventurers, but those groups can be any size to accomodate what they have to do, how many other like-minded people they found, who is their leader, and how they get along together.

So my players will encounter a company of mercenaries, or a pair of monster-hunters, or a travelling monk, or a pirate crew, or a wizard with his apprentice and a hired burly bodyguard hunting for an old book, and all of those will share a campfire with "fellow adventurers", but they will very rarely encounter a carbon copy of their "mage/cleric/thief/warrior" party. The fact that the players have that tailored group of very diverse complementary people, all willing to go to several adventures together, makes them special.

Unless there is some sort of guild/organisation/law to explain it all, having a lot of player-party-clones travelling all over the countryside looking for contracts in taverns feels very contrived.

[MonochromeTiger]

But in-world, in a classic D&D setting where "adventurers" are common enough that you can reliably head to your local tavern to tell the newest group about the goblins nearby, why wouldn't an adventuring party want to have more people? Sure, you'll consume more resources and split treasure more ways, but isn't that worth the greatly increased chances of survival, or the faster dungeon clear rate in any case? I guess a large party also makes stealth difficult, but that feels more like a "roguish party's concerns" rather than something that would really become conventional across your entire generic medieval fantasy world. If you happen to only have 3 adventure-worthy friends, then make a mini-party and meet a couple more groups of 3-4 people to team up with. Call it an alliance, or perhaps a company, or maybe even... I dunno, a fellowship?

Unless, that is, there's some kind of in-universe explanation that adventurers rarely (or never) form groups of more than 4-6. If you've got one or more you like to use, then would you mind sharing with the class?

Adventurers are weird. Even in settings where "Adventurer" is an actual job title it's not the kind of job you'd expect to really see a normal person take. Sure there are jobs that deal with violence as just part of what they do like Guard or Soldier or Mercenary but while Adventurers may take on jobs that overlap with those they're still a distinct job unique from them and personally I've always interpreted part of that as a bit of inherent strangeness compared to any of their closest counterparts. The same strangeness that contributes to someone actually eventually pulling off the goal of being "the strongest person in the country" or "undisputed master of all weapons" or "the Archwizard known throughout the land" or having their God or Goddess on speed dial. You may notice that when NPCs get that kind of power they also tend to be part of rather exclusive little clubs and not socializing much outside their limited circle of friends and family or hangers on, at least not as equals and partners in their endeavors even in the case of the "good guy" examples.

Honestly I think the standard adventuring party reflects that pretty easily and also acts as an advertisement for why larger groups may not be impossible but are kind of rare. Everybody's a little odd in one way or another, not a bad thing necessarily but enough that the typical Adventurer is probably some degree of "eccentric" by the standards of the average person. It's way easier to deal with a handful of standout personalities and the inevitable moments of friction or misunderstandings than it is to deal with twenty or more, and considering how dangerous adventuring is you kind of want to know the people with you actually have your back and aren't strange Wizard number six whose relationship with you can be summarized with "waiting for you to die so they can have a very slightly larger share."

On top of that, Adventurers may be "more common" in some settings but there's a difference between that and roving groups of adventurers numbering in the hundreds to thousands. Adventurers worth their name, especially those able to handle bigger threats, aren't something you just trip over every time you cross the room in a tavern, and if they were odds are those same taverns would be posting "clear out the Adventurer nest in the basement" jobs to deal with the constant string of parties that refuse to leave. Super common Adventurers raises the question of why there are even threats left that require Adventurers. They aren't the standard response to danger, that's Guards or in more extreme cases sending word to whatever the local government is asking for the military or a mercenary company to be sent in.