When we are thinking about stuff like embeds, we are not thinking about how we are competing with YouTube. We are thinking about how are we going to make it more useful for people to share stuff on Facebook.

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.

Just take terrorism, for example. We have a team of more than 200 people working on counterterrorism. I mean, that's pretty intense. That's not like what people think about what Facebook is.

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.

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

People love photos. Photos originally weren't that big a part of the idea for Facebook, but we just found that people really like them, so we built out this functionality.