Self-interest is the desire to act in ways that promote what is good for one’s self. Whether or not human behavior is, or perhaps more important should be, motivated by self-interest has been a central theme throughout the history of Western philosophy. The term egoism is used to describe a variety of philosophical schools of thought on the pursuit of self-interest. Some Eastern philosophies, notably Taoism and Zen Buddhism, also discuss a form of egoism—solipsism—that argues that one’s own existence or at least the experiences of one’s own existence are the only things one can truly verify.

Perhaps because of a common fear that self-interest will be pursued excessively, most religions have codes of conduct that promote regard for others. The dividing line between self-interest and ...