According to Alfred Adler, the father of individual psychology, all children feel inferior when they compare themselves to the more capable adults around them. Adler said that children strive for superiority to compensate for that inferiority felt during childhood.
According to Adler, a secondary inferiority happens when an adult finds himself far away from reaching an important psychological goal. A man who earns a low salary compared to most of his friends might develop a secondary inferiority and so strive to become superior.
Youngest children usually develop very high ambition and sometimes strive to be the best among their peers or friends.
While ordinary people usually strive to become superior, narcissists usually take that striving to an extra level. Narcissists always want to keep eyes on them by showing others how great they are, and as a result, they might strive to become more superior.
A person who develops an inferiority complex or who believes that he is inferior to others might strive to become superior to them. For example, a child with a birth defect who grew up believing that he is different in a bad way might strive more to become superior.
Many of the critical comments people make about others have the goal of putting them down. A person who feels inferior to a successful person, might make fun of him or gossip about him to feel superior to him (See why people get jealous).
According to Adler, some people strive for superiority the good way by trying to become more successful and useful to the community, while others strive for superiority the useless way by becoming neurotics or criminals.
Many people strive for superiority to prove others wrong. This usually happens with people who experience serious rejection or the ones who go through a bad rejection experience that they can't get over.
Adopted children sometimes unconsciously believe that their original parents dumped them because they believed they were worthless. When those adopted children are given the chance, they sometimes become over-achievers in life.
Only a confident and brave person strives for superiority the useful way. According to Adler, people who don't have enough courage to fight for their important goals move to the less useful side of life and usually become neurotics.
If a person is always compared to others and if he cares about the subject of the comparison, he will strive to become superior to those other people.