"regard to or pursuit of private interest, advantage to oneself," 1640s, from self- + interest (n.). Especially "selfishness, pursuit of egotistical interests to the exclusion of regard for others." Related: Self-interested, "characterized by self-interest" (1650s); self-interestedness.
[Self-interest] is a doctrine not very lofty, but clear and sure. It does not seek to attain great objects; but it attains those it aims for without too much effort. ... [It] does not produce great devotion; but it suggests little sacrifices each day; by itself it cannot make a man virtuous; but it forms a multitude of citizens who are regulated, temperate, moderate, farsighted, masters of themselves; and if it does not lead directly to virtue through the will, it brings them near to it insensibly through habits. [Alexis de Tocqueville, "Democracy in America"]
"inherent fitness for all ends and purposes and independence of others," 1620s, originally also an attribute of God (translating Greek autakreia); see self + sufficiency. Of mortals, "ability to supply one's own needs," it is implied by 1580s (compare self-sufficient). Sometimes formerly also "an overweening opinion of one's talent or worth" (1690s).