The main Facebook usage is so big. About 20 percent of the time people spend on their phone is on Facebook.

It used to be the case, like you'd switch jobs, and then maybe you wouldn't keep in touch with all the people that you knew from that old job, just because it was too hard. But one of the things that Facebook does is it makes it really easy to just stay in touch with all these people.

The thing that's been really surprising about the evolution of Facebook is - I think then, and I think now - that if we didn't do this, someone else would have done it.

You get a reputation for stability if you are stable for years.

If you're always under the pressure of real identity, I think that is somewhat of a burden.