It should go without saying that just because you and your character share the same knowledge doesn't mean you acquired it in the same way. In defense of the 'really bad' idea, I think there's much fun to be had improvising explanations for how Thag the Dumb knows enough astronomy to solve the puzzle, or how Ken the Chaste knows everything about BDSM. It's a different type of role playing, for sure, but not inherently bad.