Quote Originally Posted by Maat Mons View Post
My inclination is to say that anything called "luck" shouldn't let you get a result higher than the maximum you would otherwise be able to obtain. Instead, it should just make it more likely that you'll get the highest result you'd otherwise be able to obtain.
Agreed. I also like a simple rule rather than a Luck pool. To that end:

Luck: You can give fate a nudge to turn a failure to success. When rolling any d20, add or subtract half your luck modifier (rounded up) to the roll, to a minimum of 1 and maximum of 20. Critical successes and failures are unaffected by this, and this modifier doesn't change a dice roll into a critical success or failure.

So if you have a score of 20 and modifier of +5, you add +3 to any roll below 18 and above 1 before other modifiers. In this instance, a roll of 17, 18, 19 and 20 are counted as 20, but only a roll of 20 is critical. A roll of 2 is counted as a 5, but 1 is still a critical failure.
Likewise, if you have a Luck of 8 and modifier of -1, you subtract -1 from all rolls. A 20 is still a critical success, but everything else is slightly worse.

This stops a lucky player being able to beat a proficient one most of the time, while an unlucky player is hindered but not unplayable or at the whim of a DM. It feels a little 3.5y to be adding extra numbers, but Lck 10-11 is an opt-out if you're wanting to simplify. I'm sure there's some point buy cheese (a Luck of 6 has the same penalty as 9) that'd need balancing, but this is the easiest rule for Luck I could come up with (aside from FNVs blanket skill bump and insane crit boost)