Warbringer
Explorer
You seem to have missed that we aren't talking about rational in game reasons for it like knowledge rolls.
I was responding to ...
"A player doesn't get to suddenly decide that their grandpappy is a survivor of the underdark and at some point explained all that goes on down there to the PC..."
I presented examples (roll and inspiration) as in game mechanical reasons that refute the above. I also have no problem that a player could make that statement above (which in a game like 13th Age would be deciding a characters background - read skills). Players get to do that type of thing all the time in my world, including creating friendly NPCs, creating terrain on the battlefield, a lingering wound on a monster ... Anything the adds flavor to the story... (And yes it's an in story reason for meta game at times)
However, I have a problem with players that continually revert to meta game without creating in game coherency because I feel they're missing out on the fun of failing in a completely safe environment. There is nothing to win in D&D... Apart from the experience