Selfishness

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; and has also been contrasted (as by C. S. Lewis) with self-centredness

Divergent views

The implications of selfishness have inspired divergent views within religious, philosophical, psychological, economic and evolutionary contexts.
Classical

Aristotle joined what he saw as the majority of his countrymen in condemning for selfishness those who sought only to profit themselves; but approved the self-love of the man of reason who sought to gain for himself the greatest share of what deserved social praise.

Seneca proposed a cultivation of the self within a wider community - a care for the self which he opposed to mere selfishness in a theme that would later be taken up by Foucault.
Medieval/Renaissance

Selfishness was viewed in the Western Christian tradition as a central vice – as standing at the roots of the Seven deadly sins in the form of pride.

Francis Bacon carried forward this tradition when he characterised “Wisdom for a man's self.. s the wisdom of rats”.
Modernity

With the emergence of a commercial society, Bernard Mandeville proposed the paradox that social and economic advance depended on private vices – on what he called the sordidness of selfishness.

Adam Smith with the concept of the invisible hand saw the economic system as usefully channelling selfish self-interest to wider ends; while Locke based society upon the solitary individual, arguably opening the door for later thinkers like Ayn Rand to argue for selfishness as a social virtue and the root of social progress.

Roman Catholic philosopher Jacques Maritain opposed the latter view by way of 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 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.
Psychology

Lack of empathy has been seen as one of the roots of selfishness, extending as far as the cold manipulation of the psychopath.

The contrast between self-affirmation and selfishness has become a conflictual arena in which the respective claims of individual/community is often played out – between parents and children or men and women, for example.

Psychoanalysts favor the development of a genuine sense of self, and may even speak of a healthy selfishness, as opposed to the self-occlusion of what Anna Freud called 'emotional surrender'.
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.

Source

Wikipedia:Selfishness