in 1921 the influential psychologist Carl Jung had published a bombshell of a book, Psychological Types, popularizing the terms introvert and extrovert as the central building blocks of personality. Introverts are drawn to the inner world of thought and feeling, said Jung, extroverts to the external life of people and activities. Introverts focus on the meaning they make of the events swirling around them; extroverts plunge into the events themselves. Introverts recharge their batteries by being alone; extroverts need to recharge when they don’t socialize enough.
