The people that make a durable difference in the world are not the people who have mastered many things, but who have been mastered by one great thing. If you want your life to count . . . you don’t need to have a high IQ. You don’t have to have good looks or riches or come from a fine family or a fine school. Instead you have to know a few great, majestic, unchanging, obvious, simple, glorious things — or one great all-embracing thing — and be set on fire by them.