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.

I started designing book jackets, which was great because I was good at it. And then from there I decided to become a freelance graphic designer and I needed to expand beyond book jackets, so I taught myself web design, and then in 1999 some friends of mine decided to start a company called Xanga.com, which was a very early kind of social network slash blogging community.

I think of Twitter as a messaging system that you didn't know you needed until you had it. Think about when cell phones first started coming out. People said, "Why would I carry my phone around?" And now you'll drive back to your house thirty miles if you forget your cell phone.

When you hand good people possibility, they do great things.

What if the New York Times gave out free, cheap Kindles to everyone and said this is how we're doing it now. You know? Maybe that's a way to go. The technology gets cheaper and cheaper, and at some point it has to be cheaper than all these trucks and all this gas, to just say, let's give away a Kindle to everyone.

Have confidence in your ideas before they even exist.

We hired a CSR person at Twitter, years before we hired our first sales person, to make sure we had a culture and impact of doing good.