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.

What must underlie successful epidemics, in the end, is a bedrock belief that change is possible, that people can radically transform their behavior or beliefs in the face of the right kind of impetus.

We need to look at the subtle, the hidden, and the unspoken.

A prediction, in a field where prediction is not possible, is no more than a prejudice.

Ideas and products and messages and behaviors spread just like viruses do.

Cultural legacies are powerful forces. They have deep roots and long lives. They persist, generation after generation, virtually intact, even as the economic and social and demographic conditions that spawned them have vanished, and they play such a role in directing attitudes and behavior that we cannot make sense of our world without them.

Acquaintances represent a source of social power, and the more acquaintances you have the more powerful you are.