The fact that individuals in a market economy act so as to make themselves better off is a major reason a market equilibrium is usually efficient.

In a market economy, self-interested behavior leads individuals to pursue actions that maximize their own well-being. This behavior, in turn, leads to market outcomes that are efficient in the sense that they maximize the total benefits to society. This is because individuals who behave in their own best interests will naturally gravitate towards activities that are the most productive and valuable, since these activities offer the highest returns. As a result, resources are allocated in a way that maximizes overall social welfare, leading to an efficient market equilibrium.