"Our lives are shaped as profoundly by personality as by gender or race. And the single most important aspect of personality--the "north and south of temperament," as one scientist puts it--is where we fall on the introvert-extrovert spectrum. Our place on this continuum influences our choice of friends and mates, and how we make conversation, resolve differences, and show love. It affects the careers we choose and whether or not we succeed at them. It governs how likely we are to exercise, commit adultery, function well without sleep, learn from our mistakes, place big bets in the stock market, delay gratification, be a good leader, and ask "what if."* It's reflected in our brain pathways, neurotransmitters, and remote corners of our nervous systems. Today introversion and extroversion are two of the most exhaustively researched subjects in personality psychology, arousing the curiosity of hundreds of scientists."