In psychology, grandiosity is a sense of superiority, uniqueness, or invulnerability that is unrealistic and not based on personal capability. It may be expressed by exaggerated beliefs regarding one's abilities, the belief that few other people have anything in common with oneself, and that one can only be understood by a few, very special people. The personality trait of grandiosity is principally associated with narcissistic personality disorder (NPD), but also is a feature in the occurrence and expression of antisocial personality disorder, and the manic and hypomanic episodes of bipolar disorder.