There's no way to make that decision without the knowledge you have as a player, though. That's my point. You can't "unknow" something. So any decision you make is made with that knowledge.
This may or may not be a problem. I'm not saying that you can't reasonably surmise how a fictional character would act in a given situation. Certainly we can come up with any number of ways that a fictional person can act in a given situation.
The problem is, I think, when a GM says to a player "no, you can't do that because I've imagined a different situation". Especially since, in times where this happens, the impact is usually not of the "game ruining" level that it's often cited.
To me, it's far worse for a GM to tell a player that they can't do something that their character could conceivably do than for a player to blast a troll with a scorching ray even though he's never encountered a troll before.
One of these things seems far more disruptive to play than the other.