I mean, we've built a lot of products that we think are good, and will help people share photos and share videos and write messages to each other. But it's really all about how people are spreading Facebook around the world in all these different countries. And that's what's so amazing about the scale that it's at today.

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.

Advertising works most effectively when it's in line with what people are already trying to do. And people are trying to communicate in a certain way on Facebook - they share information with their friends, they learn about what their friends are doing - so there's really a whole new opportunity for a new type of advertising model within that.

We just think that there are all these different ways that people want to share, and that compressing them all into a single blue app is not the right format of the future.

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