But for situations where there are thing the characters can’t observe? When characters don’t have complete awareness of all the external factors, so the players don’t act on information their characters couldn’t have.
Reusing my guard example from the initial post, you try to bluff the guard that “you’re just travellers” you roll a 3 on deception, you see you have a 3, but then the guard says with a smile “welcome, come on in, you must be tired after such a long journey on the roads”, doesn’t that make you immediately suspicious knowing you rolled a 3? suspicious in a way you wouldn’t be if you didn’t know the results of your roll, and no matter how much you might try to ignore that information as you describe your actions it’s still going to be there in your mind influencing your thought process whether you want it to or not.