There's a difference between being obsessed and being motivated.

There are a few other things that I built when I was at Harvard that were kind of smaller versions of Facebook.

Facebook is uniquely positioned to answer questions that people have, like, what sushi restaurants have my friends gone to in New York lately and liked? These are queries you could potentially do with Facebook that you couldn't do with anything else, we just have to do it.

What Facebook stands for in the world is giving people a voice and spreading ideas and rationalism.

If you live in an area where there is not a good school, the internet may be the best way to get access to a lot of education material. The same is true if there is not a good doctor - the internet may be the best way to get access to health.

We want Facebook to be one of the best places people can go to learn how to build stuff. If you want to build a company, nothing better than jumping in and trying to build one. But Facebook is also great for entrepreneurs/hackers. If people want to come for a few years and move on and build something great, that's something we're proud of.

The world is changing so quickly, with mobile stuff and different platforms emerging, that I think it's more likely that the biggest competitor for Facebook is someone that we haven't heard of. What that means for us is that we should just really stay focused on what we're doing.