Facebook originally got started around the same time as a bunch of the early smartphones and those platforms got started. So we didn't really get to play any role in developing that platform.

We're a community of a billion-plus people, and the best-selling phones - apart from the iPhone - can sell 10, 20 million. If we did build a phone, we'd only reach 1 or 2 percent of our users. That doesn't do anything awesome for us. We wanted to turn as many phones as possible into 'Facebook phones.' That's what Facebook Home is.

Our role is to be a platform for making all of these apps more social, and it's kind of an extension of what we see happening on the web, with the exception of mobile, which I think will be even more important than the web in a few years - maybe even sooner.

If we're trying to build a world-class News Feed and a world-class messaging product and a world-class search product and a world-class ad system, and invent virtual reality and build drones, I can't write every line of code. I can't write any lines of code.

We think the fact that Instagram is connected to other services beyond Facebook is an important part of the experience...This is an important milestone for Facebook because it's the first time we've ever acquired a product and company with so many users.

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.