Clive Thompson:

People weren't just getting fatter randomly.

Good behaviors -- like quitting smoking or staying slender or being happy -- pass from friend to friend almost as if they were contagious viruses.

And the same is true of bad behaviors -- clusters of friends appear to "infect" each other with obesity, unhappiness and smoking.

People may be able to pass along a social signal without themselves acting on it.

Nicholas A. Christakis & James Fowler:

Your colleague's husband's sister can make you fat, even if you don't know her.

Christakis:

It turns out that all kinds of things, many of them quite unexpected, can flow through social networks.

Christakis & Fowler:

Each additional happy friend increases a person's probability of being happy by about 9%.

Sandy Pentland:

You couldn't prove what they say, but I happen to believe it.

Subtle patterns in how we interact with other people reveal our attitudes toward them.

Nora Johnson:

In our unending search for panaceas, we believe that happiness and "success" -- which, loosely translated, means money -- are the things to strive for. People are constantly surprised that, even though they have acquired material things, discontent still gnaws.

Pico Iyer:

It seems that happiness, like peace or passion, comes most freely when it isn't pursued.

Thompson:

Your place in the network affects your happiness, but your happiness doesn't affect your place in the network.