also self interest, 1640s, from self- + interest (n.). Related: Self-interested.
[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"]