Of all the concepts Carl Jung introduced into psychology and culture, the distinction between introversion and extraversion has traveled furthest from its origin. These two words are now used so casually, so universally, and with such confidence that most people assume they understand them. They assume introversion means shyness and extraversion means sociability, that the introvert prefers to be alone and the extravert prefers company, that these are essentially descriptions of social preference. This popular understanding is not entirely wrong. It is profoundly incomplete. Jung’s original theory of psychological types is one of the most sophisticated and clinically precise frameworks...