hawkeyefan
Legend
Plus let's be honest. If you fight a werewolf without silver or a mummy without fire, what the heck are you supposed to do? Die?*
*Ok, granted, you could flee, but a werewolf can probably catch you, and, depending on the edition, fleeing is a lot harder than it sounds. in AD&D you open yourself up to a free hit, in 3.x the Run action lowers defenses -and- provokes, and the same might be true for players taking the Dash action in 5e. This is why in 3e I usually kept an Obscuring Mist or similar spell prepared.
Right. I think it's dull and silly to ask or expect players not to use their knowledge in those situations. The issue in those cases is the decision to use those monsters. If I use trolls in my game, it's about "can the PCs beat these trolls" not "can the players pretend to not know that fire will help them beat the trolls". As a GM, I'm not focusing on the deployment of fire as problematic in any way. The only way a scenario where there's a monster with an unknown weakness can be interesting is that first time, when no one actually knows the weakness. After that, you need to find other ways to make the monster interesting.
Metagaming is always present. It's not avoidable. What I think is interesting is how it affects play, and what is considered acceptable or unacceptable to individuals and why.