Neither is the character using knowledge it does not have. That's as much of an option as poofing into a god.
No, it's different. The second level fighter Jezal being played by 38 year old player Tony, who has been playing D&D for 30 years, may actually know that Trolls are vulnerable to fire. Unless Tony and the DM have a comprehensive list of all the things Jezal knows and a list of what he doesn't know, then it's actually a gray area at the time the troll shows up in the game.
So the DM decides on the spot that Jezal does not know about trolls. This is the DM removing options from the player.
Those don't exist in isolation. What the character knows or does not know is a part of whether or not something is an option.
Sure. And there are times when it's very clear what the character knows or doesn't know...and there are other times where it is not so clear, correct?
No. Cheating is not an option.
This doesn't answer the question. I have since elaborated, so maybe now it is clearer.
Do you see the DM's decision to determine on the spot that Jezal does not know about trolls as limiting Tony's choices as a player? Tony hadn't made a decision what to do yet...we're just looking at the choices available to him. Has the DM limited those choices?
Immersion can be fun, sure. But it isn't a guarantee of fun. Hence my example of a boring encounter with nothing going for it but the "mystery" of how to hurt trolls.
So, given the choice between immersion and fun, I would say fun is the more important element to maintain.
It matters for every decision. A troll and fire is no different from any other situation where the player has knowledge the PC doesn't have.
Except something like "what's in the next room" when the players have no clues to tell them is easy to determine. If Jezal knows about trolls and fire is not so easy to determine. Folklore would exist in his world. Perhaps he had a cousin who faced a troll once.
Because it involves backstory beyond the scope of the game events it is much harder to determine definitively.
So there is a difference.
I've never been able to do it accidentally.
I'm not sure I understand what you mean here. Do you mean you've never accidentally acted on meta-knowledge?
Encounters are part of the developing story of the game, and often encounters are a part of the character's role. Take a giant hunter. Encounters with giants are a very large part of his role and story.
I agree by the way that there should be other interesting things. I just don't agree that it's okay for the PC to have all the knowledge of monsters that the player does.
Sure, I can understand that. I'd say the best way to counter this is to change the monsters up and keep your players guessing rather than having them pretend to not know things they know.
I'm not sure where you got the idea that the weakness was the only thing going for the encounter. Those other things just don't make it okay to metagame.
I think I explained this above....immersion in and of itself does not equal fun. But also because if there is more to an encounter...if it's dynamic and has some cool elements...then the matter of Tony having Jezal break out the oil against the trolls is less of a big deal. It doesn't undermine the point of the encounter. It isn't as big a deal to let it slide.
That's not true. I don't do anything other than ask, "What would my character do." What my character would do is based on what he knows. I don't even consider things that he doesn't know, and if it's something he might know, I generally get a roll for it.
I'm speaking from the DM perspective on this. The DM is as familiar with the characters as the players. So creating encounters that hinge upon the disparity between player knowledge and character knowledge is probably a bad idea. Better to design the encounter differently. That's what I meant about avoiding that wrinkle. This is where the DM contributing to metagaming comes into it.
I've not encountered that wrinkle. I know my character, his background, skills, prior encounters, etc. It's simplicity to just act on what he does know.
But there's no way to have an accurate tally of what he knows.
I suppose Skill Checks could serve to help in the gray areas...but I would think that simply allowing PCs to know that trolls are vulnerable to fure is fine. It's no less arbitrary than deciding that they don't know. And more importantly, it keeps the game moving along.