That's actually very helpful! If you need to go to the dentist or something and you convince yourself that it's not going to hurt at all it might still hurt but a lot less than if you were panicking the whole week worried about how much it's going to hurt
But the opposite can work too, you get ready for the pain to be a 9 but it only hurts a 7 so it feels like a 5
So, remember kids: Lie to yourselves B)