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.

Quiet: The Power of Introverts in a World That Can't Stop Talking (ed. Penguin UK, 2012) - ISBN: 9780141970172