The Rule of 150 says that congregants of a rapidly expanding church, or the members of a social club, or anyone in a group activity banking on the epidemic spread of shared ideals needs to be particularly cognizant of the perils of the bigness. Crossing the 150 line is a small change that can make a big difference.

If your parents are billionaires, that might actually be an obstacle to your own happiness and self-development. If you go to Oxford or Harvard, that might actually thwart your desire to graduate with a science or math degree.

It's not how much money we make that ultimately makes us happy between nine and five. It's whether or not our work fulfills us. Being a teacher is meaningful.

Living a long life, the conventional wisdom at the time said, depended to a great extent on who we were-that is, our genes. It depended on the decisions we made-on what we chose to eat, and how much we chose to exercise, and how effectively we were treated by the medical system. No one was used to thinking about health in terms of community.

People who bring transformative change have courage, know how to re-frame the problem and have a sense of urgency.

I think that persistence and stubbornness and hard work are probably, at the end of the day, more important than the willingness to take a risk.

Success is not a function of individual talent. It's the steady accumulation of advantages. It's bound up in so many other broader circumstantial, environmental, historical, and cultural factors.