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Selfishness is placing concern with oneself or one's own interests above the well-being or interests of others. Selfishness is the opposite of altruism or selflessness.
Game theory 
Main article: game theory
Given two actors, oneself and someone else, there are four types of possible behavior directly impacting the welfare of the actors: selfishness, altruism, spite, and cooperation. Selfishness is harming someone else in order to help oneself; altruism is harming oneself in order to help someone else; spite is harming oneself in order to harm someone else; cooperation is helping someone else and also helping oneself. 
The implications of selfishness have inspired divergent views within religious, philosophical, psychological, economic and evolutionary contexts. For example, Roman Catholic philosopher Jacques Maritain, in The Person and the Common Good, made the Aristotelian argument that framing the fundamental question of politics as a choice between altruism and selfishness is a basic and harmful mistake of modern states. Rather, cooperation in a sense similar to the game theory usage above ought to be the norm: human beings are by nature social animals, and so individual persons can only find their full good in and through pursuing the good of the community.
See also 
Further reading