“a key component of the brain’s dopamine-driven reward system, is larger in extroverts than in introverts. Introverts “have a smaller response” in the reward system, writes psychologist Nettle, “and so go less out of their way to follow up [reward] cues.” They will, “like anyone, be drawn from time to time to sex, and parties, and status, but the kick they get will be relatively small, so they are not going to break a leg to get there.” Excerpt From Quiet by Susan Cain