The core of mainstream economics is rational choice theory. According to this theory, the guiding principle of human behavior and decision making is that individuals maximize their own self-interest.
Rational choice theory provides the foundation for the idea that for-profit businesses maximize profits and efficiency. Profit is the ultimate goal, but in a competitive market the surest way to maximize profits it to maximize the efficiency of the business. Competitive discipline plus rational choice results in organizational efficiency.
As critics have long pointed out, rational choice theory is based on heroic assumptions: that individuals have perfect information and computerlike information processing capability, which are used to maximize utility. Economists justify maintaining these assumptions because rational choice models allegedly produce accurate predictions. (They don’t, but that’s another story.)