The field of psychology has focused disproportionate on all that’s negative about human nature. Psychologists should devote more energy to studying the roots of human happiness, virtue, and well-being. Over the past six years, a growing number of psychologists have embraced this view of their field—a view often identified with the “positive psychology” movement and one of its chief proponents, former American Psychological Association President Martin Seligman. But even as the tenets of...