The lesson here is very simple. But it is striking how often it is overlooked. We are so caught in the myths of the best and the brightest and the self-made that we think outliers spring naturally from the earth. We look at the young Bill Gates and marvel that our world allowed that thirteen-year-old to become a fabulously successful entrepreneur. But that's the wrong lesson. Our world only allowed one thirteen-year-old unlimited access to a time sharing terminal in 1968. If a million teenagers had been given the same opportunity, how many more Microsofts would we have today?

A study at the University of Utah found that if you ask someone why he is friendly with someone else, he’ll say it is because he and his friend share similar attitudes. But if you actually quiz the two of them on their attitudes, you’ll find out that what they actually share is similar activities. We’re friends with the people we do things with, as much as we are with the people we resemble. We don’t seek out friends, in other words. We associate with the people who occupy the same small, physical spaces that we do.

The single most important thing a city can do is provide a community where interesting, smart people want to live with their families.

If we think about emotion this way - as outside-in, not inside out - it is possible to understand how some people can have an enormous amount of influence over others. Some of us, after all, are very good at expressiing emotions and feelings, which means that we are far more emotionally contagious than the rest of us.

Policy is driven by more than politics, however. It is equally driven by ideas.

Economists often talk about the 80/20 Principle, which is the idea that in any situation roughly 80 percent of the “work” will be done by 20 percent of the participants. In most societies, 20 percent of criminals commit 80 percent of crimes. Twenty percent of motorists cause 80 percent of all accidents. Twenty percent of beer drinkers drink 80 percent of all beer. When it comes to epidemics, though, this disproportionality becomes even more extreme: a tiny percentage of people do the majority of the work.

If you are going to do something truly innovative, you have to be someone who does not value social approval. You can't need social approval to go forward. Otherwise, how would you ever do the thing that you are doing?