I'm just going to add this because I think sometimes this might not be so self-evident:
You are not trying to make the right decision against this one villain in this hand. You are trying to make the right decision against all villains that play similarly, and against the range of hands they can have.
You're not trying to figure out if he's holding QK or QJ here, you're trying to figure out what % of times he has either one of these hands, and make a decision that is correct against the sum of all possible scenarios.