What if it IS what my character would do?

[OldTrees1]

Yes, sometimes.

But not in the scenario I described.

In this scenario, the GM made design to change the rules of engagement for the campaign midway through while giving neither hints in-game or statements in real life that the rules had changed. The player who continued to act the way they acted the entire game with no complaints bears no responsibility for the fallout. It s not like he can read the GM's mind.

If I were the player, then despite the lack of forewarning I would accept some of the responsibility because my continued actions contributed to the issue, even if the GM is 100% to blame. I would work with the GM to resolve the fallout.

In the scenario you describe, I can see some hints with the benefits of 20-20 hindsight. So I would accept even more responsibility and be even more committed to working to resolve the fallout.

Situations like this take 2 people and since I control myself, I should think of it as always being at least a bit my responsibility , even if it is also 100% the other person's fault. Fault/responsibility is not conserved.

I would also like to echo my earlier point-namely, why assign blame?

Unless you're looking to scapegoat a victim or something, it's more important to just make the game better.

A very good point. I can think of only 1 reason:
Who can do something differently next time? Usually multiple people have that opportunity. Usually I have that opportunity.