I can unpack a little: I pay attention to beliefs and instincts (especially for characters that last more than one session), but I actively discourage players from telling me their goals.
I view my job as fairly representing the play location (generally the dungeon), the inhabitants and their reactions to the characters’ actions. They shift naturalistically in response to the characters’ actions, but not in response to the players’ actions. For example, if I’ve put giant frogs in the moat near the entrance to the dungeon and the players cleverly avoid that entrance, skirt the moat and enter the dungeon another way, I won’t move the giant frogs to another location to force the encounter. The players earned their success. On the other hand, if the characters wind up making a lot of noise and warn the monsters of their approach, I’ll have the monsters react – moving to more defensible locations and concentrating their numbers.
In the same way, I don’t want to tempt myself to ramp up the opposition just because a player found a clever way to approach her goal and bypassed the trap or monsters that I thought they would struggle with.