Why do policies and business practices that ignore the moral and generous side of human nature often fail?

Should the idea of economic man--the amoral and self-interested Homo economicus--determine how we expect people to respond to monetary rewards, punishments, and other incentives? Samuel Bowles answers with a resounding "no." Policies that follow from this paradigm, he shows, may "crowd out" ethical and generous motives and thus backfire.

But incentives per se are not really the culprit. Bowles shows that crowding out occurs when the message conveyed...