“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.”

This quotation emphasizes one of the book’s main themes, the Genetic Origins of Introversion. The author wants to make it clear from the start that personality is part of one’s makeup, deeply embedded in what makes up identity. The passage also shows how thoroughly personality affects everything in our lives.

“Introversion—along with its cousins sensitivity, seriousness, and shyness—is now a second-class personality trait, somewhere between a disappointment and a pathology. Introverts living under the Extrovert Ideal are like women in a man’s world, discounted because of a trait that goes to the core of who they are. Extroversion is an enormously appealing personality style, but we’ve turned it into an oppressive standard to which most of us feel we must conform.”

This touches on another theme, the Extrovert Ideal in American Society. Cain’s premise in the book is that introversion has not just been overlooked, but that it has also been degraded to the point that it is seen as an embarrassment, or worse. Her goal is to redeem this personality type, which a third to a half of the population belongs to, and show that it has value equal to that of extroversion.

“Carnegie’s metamorphosis from farmboy to salesman to public-speaking icon is also the story of the rise of the Extrovert Ideal. Carnegie’s journey reflected a cultural evolution that reached a tipping point around the turn of the twentieth century, changing forever who we are and whom we admire, how we act at job interviews and what we look for in an employee, how we court our mates and raise our children. America had shifted from what the influential cultural historian Warren Susman called a Culture of Character to a Culture of Personality—and opened up a Pandora’s Box of personal anxieties from which we would never quite recover.”

Here Cain refers to Dale Carnegie, whose life story is inextricably intertwined with the rise of the Extrovert Ideal. Carnegie transformed himself from a shy country boy into a gregarious, confident peddler of public speaking within the span of a decade. His books and public lectures were a large part of the trend at the beginning of the 20th century toward the idea that