During one of the latest sessions something interesting happened: one of the characters developed an intense hatred for an NPC but the player kept for himself that until, out of the blue, attacked the NPC with murderous intent, taking everyone by surprise.
Everyone. Storyteller and other players included.
Fast-forward to the post-session chit-chat, the player kept everything for himself because telling the thing was, in his opinion, metagame and it would have been wrong.
From there, we had an interesting talk, which made me think.
What’s this metagame thing?
Metagame is a broad concept, I can sum it up with “when a character acts because of knowledge his player has but he doesn’t”.
This kind of behaviour includes stuff within an astronomically broad border: heroes who attacks trolls with fire even if they never heard about trolls, different behaviour with PCs and NPCs, knowing that mechanically nothing can interfere with the precision of my fireball spell an placing it with dead eye accuracy, believing that if something inconsistent happens it’s DM’s fault and not a clue.
The extent is limitless and, as you can see, consequences are very different as well.
So it’s good to sort it out.
When you should avoid metagame?
The answer is obvious: when it spoils the game.
I can hear the choir of “Oh, rly?” reverberating in space so, ok, let’s be more accurate: usually a story is set up by a conflict and what happens is usually
- discovery of the conflict
- investigation
- solution
- aftermath
Investigation is usually the juicy part of the story, when the heroes know the problem and they are looking for a solution.
If the investigation comes late the story is slow-paced, if it’s over too soon it leaves you dissatisfied.
And here is the point where metagame can hurt: if a character acts pointing straight to the solution because the player already knows it, the investigation part crumbles and the story is crippled.
This applies both to a long sequence and to a simple combat encounter: if the character is supposed to not know that green faery trolls are vulnerable only when there is loud noise and at first sight he starts clashing his sword on the shield to lower his defenses, the combat encounter shifts from a challenge to a nuisance, losing his impact on the story both from a game viewpoint – resource use is lowered and management is easier – and a story viewpoint – the characters had no real event that let them learn something.
So metagame is always bad, isn’t it?
Of course not.
From the previous answer, metagame can help the story: normal stuff is boring and a good storyteller underlines everything that can be beyond normal stuff. If the storyteller underlines that the room has green drapes, these green drapes are there to be used, with creativity.

The very actions players take on items underlined in the description is metagame. As much as saying out loud an inner monologue, because other players can prepare themselves or try to intervene. But that is not wrong at all: characters should be surprised, but players don’t have to because they can think how their character reacts when surprised.
I mean, I can role an always alert character with lightning reflexes, but I’m not and I need time to put myself together and think what he would do: metagame allows me to do that.
Moreover, I mean, metagame it’s awesome for a lighthearted mood

How do you use metagame?