The modern self-help industry is built almost entirely on the logic of positive thinking. Visualize success. Picture your goals as already achieved. Fill your mind with images of what you want and trust the universe to deliver. The implicit premise of this approach is that the human mind functions best when oriented toward positive futures and that contemplating negative outcomes is psychologically dangerous, a gateway to anxiety, pessimism, and self-fulfilling failure. The Stoics thought the opposite, and on this point two thousand years of accumulated human experience and a growing body of modern psychological research suggest the Stoics were right....