Originally Posted by navar100
Reverse metagaming. There are things the characters know that the players don't. Because the players don't know, they don't even know they should be asking if their characters know so they don't even attempt to make a case for knowing something.
"You see strange glowing symbols on the wall."
"Okay, I roll Knowledge (Arcana) to see if I know anything about them."
The problem with this is the DM has probably already decided what they want you to know about the strange glowing symbols and what they don't. And if there's something that actually matters in it like a critical plot clue or something, they're not gonna leave that up to the roll of the dice.
"Whoops! Looks like you failed your Heraldic Lore check, so those guys you attacked were actually your allies. Now both the incumbents AND the rebels want you dead! Have fun!"