How do you keep players from using out of game knowledge when their characters wouldn't know the answer?

Question

A lot of times I find my players using their knowledge about the game to there characters advantage even when the characters would have no way of knowing certain information.

Here is an example. Trolls do not regenerate when struck by acid or fire damage. A lot of times I find that my characters always carry around a vial of acid or a fire spell just in case they meet a troll.

Another example would be when the characters find a portal that is blood red, a player will say, "That portal will take us to the Abyss!!" and BAM the surprise is gone.

There's more but I'm not going to make a huge list of examples. I mean I'm really glad that my players take the time to read up on this stuff but sometimes it ruins the suspense and belief of the game, I mean how would a half Orc barbarian know that a certain marking on a wand means its a Wand of Burning Hands?

My question is this: How do you get players to use character knowledge instead of player knowledge?

This question seems related How do you discourage "player knowledge" as a GM?

That question seems to be more of a "How to get players to stay in character and not Meta-Game" my players don't Meta-Game, they just forget that player knowledge is separate from character knowledge.

Answer 1

There are several things you can try:

Reflavor to hide obvious clues

I GM in homebrew worlds, so I will often reflavor monsters, spell effects, etc to fit my needs. This has the handy side effect of meaning players who can recite the stat sheet of a typical troll are unlikely to realize that the shambling swamp beast they've encountered is, in fact, a typical troll. Likewise, if all portals are blue due to how the spells were created way back when, then the players can never know whether they're going to the Astral Sea or the Abyss just by looking.

Misdirect

This one was mentioned in the linked answer, but to expand on the idea: Have your villains use intelligence when building traps. They might place some really obvious-looking gargoyles by the doors, only for the actual trap to be a pair of living trees. In one game where I was a player, the DM sent us into a library to kill a villain's familiar. The party wizard looked around, spotted a spell scroll he'd wanted for a while, grabbed it, and immediately cast it. Guess what - it wasn't the spell he thought it was, and it turned him into a mouse - just as we were being attacked by a giant cat.

Enforce limited knowledge through notes and whispers

I keep a blank notebook on hand when I'm DMing to write notes that I can pass to individual players, if I want to hand out information that one character would know but the rest wouldn't. If a couple of people know, or if it's an extended scene, I might step outside to another room with the player(s). This ensures other players won't get that knowledge, and also encourages the in-the-know player(s) to share their knowledge appropriately (or hoard it, depending on the character).

Call them out

If a player tries to use out-of-game knowledge, ask them to explain how their character knows it. If they can come up with something like Dale M's experience - perhaps they lived in an area often attacked by trolls - then great, you can move on, and now you can also play up that part of their backstory. If they don't have a good reason, they'll get the hint pretty quickly.

Let it go

In my group, there's four of us that have traded off DMing at various times. We all know the monsters and the other rules/situations pretty well. When one of us recognizes a monster, it's sometimes very hard to deliberately leave ourselves open to an ability we know about, just because it's not likely our characters would have seen it before. This is because it's no fun to lose when you know the answer - so as a GM, just let these instances go. Yeah, it's a little unrealistic, but what's more important: strict realism and adherence to knowledge rules, or having fun and kicking monster butt?

Answer 2

While I agree that meta-gaming is a potential problem, I don't think that the examples you cite are examples.

I live on the east coast of Australia. I can tell on sight the difference between a huntsman (large, scary-looking spider that is completely harmless) and a funnelweb (similar looking, large, scary-looking spider that is potentially lethal). I don't know how or when I learnt this. Is this therefore an example of meta-living?

My point is that if I grew up in a world with trolls instead of funnelwebs I may well have had a father, uncle, minstrel etc. who told me their vulnerabilities. The same holds for portals etc. The character's grew up in that world and will have a whole raft of knowledge that comes from doing that.

Now ... maybe what I think I know isn't the truth; the world is full of misinformation and old-wives tales. Maybe they are right about a troll's acid vulnerability but the fire thing got garbled and it actually heals them, it's cold that hurts your trolls.

This is a trick to be used sparingly but a little goes a long way. So long as you are consistent (i.e. trolls are always like this), and reasonably explain why what they thought they knew was wrong, your players now have cause to doubt ALL meta-game knowledge.

Answer 3

It sounds like your players are at least attempting to act in-character. You want them to act in-character as well, but their use of information learned outside of the game (or in previous campaigns) gets in the way of that.

Your first step should be to talk to the players about it. Do they agree that it's a problem? As Dale M mentioned in his answer, characters native to a world should be expected to know some things about it - It may be that your players have a different expectation about how much their characters should plausibly know. If that's the case, you should talk it over with them and try and find a place to draw the line that you can all agree with.

It's also possible that your players are trying to use information they learned in earlier campaigns because pretending not to know something isn't an activity they find fun. (It does tend to eliminate the thrill of discovery and experimentation if you know the outcome from the outset.) Again, you should probably talk it over with them if this is the case... Or you can arrange that the situations and monsters that come up in play are ones they're not familiar with, so they get to experience that thrill of discovery again. (Making up your own monsters or modifying existing ones is one of the traditional ways to do this.)

If it turns out that your players are doing it accidentally, and would have no objection to maintaining separation of in-character and out-of-character knowledge if only they could manage it, then the best solution is to get into the habit of asking "How do you know that?" Not only does this let players know when they're using knowledge they shouldn't have, but it forces them to keep track of what they know, instead of you having to remember it all.

That's about it, really. TL;DR: Check if your players are doing it deliberately. If they are, find out why and figure out a compromise. If they aren't, help them help you to solve the problem.