I don't know about you, but I am far more likely to believe something negative about myself than something positive. I accept something nice my friends say about me as empty, obligatory flattery. When someone has something cruel about me I accept it as the ugly truth.
There have been times when I've been selfish, lazy, or uncaring, but there have also been times when I've been kind, caring, and helpful. So why do I take the ugly moments to heart as what I really am? Right now I'm working to change the way I look at myself.