This is only my opinion.... I believe that bullys pick on people because they are jealous of the person they are picking on. Letting them get you upset is what they want. If more parents whould pay attention to there kids there would be less bullys.
Not letting the bully get to you will show them you could careless what they think or say. Make sure you report a bully even if its not you being picked on. So many commit suicide over being picked on when it could have been stopped jus by someone stepping up speaking out about the bully.