It starts off like a high school dance where everyone is a wall flower and nobody gets involved. Then someone secure in themselves or nutty in the head, starts to dance and everyone joins in.
In the case of the pity party, everyone starts slamming you. Suddenly you realize you don't like it and you start getting mad. Now you invited everyone to the party and now you want them to quit and go home. You should have never started this in the first place.
It is all right to feel down when you make mistakes. It is a sign of high moral character when you can admit them. The challenge is doing it in such an way that it breeds learning and future success. Don't let a mistake stop you permanently. How you come back from a set back makes a difference. Failure is an event not a life style.