Social hypochondria is the national disease of the most successful nation. By most indexes, life has improved beyond the dreams of even very recent generations. Yet many Americans, impervious to abundant data and personal experiences, insist that progress is a chimera. Gregg Easterbrook's impressive new book, ''The Progress Paradox: How Life Gets Better While People Feel Worse,'' explains this perversity. Easterbrook, a Washington journalist and fellow of the Brookings Institution, assaults readers with good news: American life expectancy has dramatically increased in a century, from 47 to 77 years. Our great-great-grandparents all knew someone who died of some disease we...