The holiday season poses a psychological conundrum. Its defining sentiment, of course, is joy—yet the strenuous effort to be joyous seems to make many of us miserable. It's hard to be happy in overcrowded airport lounges or while you're trying to stay civil for days on end with relatives who stretch your patience.

So to cope with the holidays, magazines and others are advising us to "think positive"—the same advice, in other words, that Norman Vincent Peale, author of "The Power...