Your tendency to be inward-directed or outward-directed is huge; it governs every part of the way you live and work and love.

All personality traits have their good side and their bad side. But for a long time, we've seen introversion only through its negative side and extroversion mostly through its positive side.

Schwartz's research suggests something important: we can stretch our personalities, but only up to a point. Our inborn temperaments influence us, regardless of the lives we lead. A sizeable part of who we are is ordained by our genes, by our brains, by our nervous systems. And yet the elasticity that Schwartz found in some of the high-reactive teens also suggests the converse: we have free will and can use it to shape our personalities.

We don't need giant personalities to transform companies. We need leaders who build not their own egos but the institutions they run.

As a young boy, Charles Darwin made friends easily but preferred to spend his time taking long, solitary nature walks. (As an adult he was no different. “My dear Mr. Babbage,” he wrote to the famous mathematician who had invited him to a dinner party, “I am very much obliged to you for sending me cards for your parties, but I am afraid of accepting them, for I should meet some people there, to whom I have sworn by all the saints in Heaven, I never go out.”)

In a way, education by its nature favours the extrovert because you are taking kids and putting them into a big classroom, which is automatically going to be a high-stimulation environment. Probably the best way of teaching in general is one on one, but that's not something everyone can afford.

Introverts, in contrast, may have strong social skills and enjoy parties and business meetings, but after a while wish they were home in their pajamas. They prefer to devote their social energies to close friends, colleagues, and family. They listen more than they talk, think before they speak, and often feel as if they express themselves better in writing than in conversation. They tend to dislike conflict. Many have a horror of small talk, but enjoy deep discussions.