In antiquity the Oracle at Delphi urged each to "know thyself." Socrates followed with the observation that "The unexamined life is not worth living." Aristotle called for a balance in creating the "good life" centering on the "golden mean." In the second century A.D. Marcus Aurelius, emperor of the Roman empire (the closest the western world may have ever come to a philosopher king), reminded himself in his Meditations that, "We are troubled not by the things of the world but, rather, by our perception of those things." Much more recently philosopher William James stated something similar by suggesting that the most important discovery in psychology of his day is that by changing the interior states of our minds, we can change the exterior dimensions of our lives. And, of course, Norman Vincent Peale influenced millions through The Power of Positive Thinking.