As a rule, professionals have no idea why narcissistic personality disorder takes place. Its sources are difficult to identify. When specific bio and genetic factors unite, they may influence the person’s behavior and mood adversely. Besides, it also depends on the way the child was growing and treated by parents. Usually, such people lack attention and appreciation, and everyone wants to be loved. Bullying at school may also turn a person into the selfish and boastful individual who just tries to survive this way.