Even though running is physically straining, it's mentally refreshing. Especially when you feel like you've accomplished something.

We did Twitter, and Twitter grew so fast, and in 2006 we spun it out into Twitter, Inc.

You have to think for an email. What's the subject? What's it about? It takes two seconds to think about that. So you have to think, Is this a work thing or a social thing? Which? Then you get into a situation that you don't want to be in, because then people are thinking about it too much.

You can shut down a service, and yet people will find ways to communicate.

Have confidence in your ideas before they even exist.

I don't think of Twitter as a social network. I think of it as a messaging system that has a lot of social components to it.

Embrace your constraints. They are provocative. They are challenging. They wake you up. They make you more creative. They make you better.