Who are you? It's the most fundamental of human questions. Are you the type of person who tilts at windmills, or the one who prefers to view them from the comfort of an air-conditioned motorcoach? Our personalities are endlessly fascinating--not just to ourselves but also to our spouses, our parents, our children, our co-workers, our neighbors. As a highly social species, humans have to navigate among an astonishing variety of personalities...