/sigh, Poli is right, Self-confidence from a psychological stand point is MUCH more important than self-esteem, self-esteem grows from self-confidence and self-worth which a person has to earn. There is too much focus on upping one's self-esteem without teaching them how to develop their self-worth and self-confidence. Both of these are developed through success as well as failure. When we don't teach kids how to face failure and success in positive ways and demand that they only know success it warps their perception of life and we have the idiocy that we have today.
Further - Self esteem says to the fat kid - the other kids think I'm fat and make fun of me so I must be of less worth. Self worth says to the fat kid - you are someone. you have X,Y, and Z going for you - who gives a shit what the other kids think? But he's not going to admit the difference so why bother?
Stand up for what is right, even if you have to stand alone.