The unsupervised learning is the way most people will learn in the future. You have this model of how the world works in your head and you're refining it to predict what you think is going to happen in the future.

If we want to have the biggest impact, the best way to do this is to make sure we always focus on solving the most important problems.

Facebook is inherently viral. There are lots of sites that include a contact importer, and for lots of them it doesn't really make sense. For Facebook it fits so well. It wasn't until a few years in that we started building some tools that made it easier to import friends to the site. That was a huge thing that spiked growth.

People influence people. Nothing influences people more than a recommendation from a trusted friend. A trusted referral influences people more than the best broadcast message. A trusted referral is the Holy Grail of advertising.

I think that more flow of information, the ability to stay connected to more people makes people more effective as people. And I mean, that's true socially. It makes you have more fun, right. It feels better to be more connected to all these people. You have a richer life.

If the original Facebook was the first five minutes [of a conversation] and the stream was the next 15, what I want to show you today is the rest-the next few hours of a deep engaging conversation.

Of course the Silicon Valley is unique and Berlin is not yet comparable. But of all the different cities that are building a startup infrastructure, Berlin is the one with the most similar energy.