Interviewer (Sam Altman): You were 19 when you started Facebook. One of the questions we hear a lot at Y Combinator is: “I’m 19 today and I really want to do everything I can to make the world a better place. What should I do?” So, what advice would you give to people who are 19 now and want to make an impact like you did?

Mark Zuckerberg: You know, I’ve always thought that the most important thing entrepreneurs should do is pick something that really matters to them and work on it—but not commit to turning it into a company until it truly proves itself. And if you look at the history of the best companies that have been built, I really believe a remarkable number of them were started this way—not by people who set out from day one deciding they wanted to start a company. Because if you do that, you often get stuck in a kind of “local maximum.”

Interviewer: I completely agree. And just to clarify, how long after launching Facebook did it officially become a company?

Mark Zuckerberg: Um… I’m not sure. I think it was probably around six months after we started, when Peter Thiel invested. That’s when it was formally incorporated in Delaware. When we first spoke with Peter about raising money, Dustin and I were very upfront with him—we told him we planned to go back to school. You know, I was a sophomore when I started Facebook. We spent the summer working on it full-time since there were no classes, but the plan was to return to Harvard in the fall and keep working on it, though not sitting in an office and doing it full-time. And Peter was like, “Yeah, sure, you’ll go back.” I guess he knew better than we did.

Interviewer: So you think he didn’t really believe you would go back to school?

Mark Zuckerberg: Yeah, I’m sure he didn’t.

Interviewer: Well, I’ll have to ask him myself—we’re interviewing him in this series too.

Mark Zuckerberg: I think he’d probably say he knew we wouldn’t go back, or at least believed he could convince us otherwise. But he never needed to. It became obvious very quickly that the workload was growing fast. Still, we didn’t drop out immediately. We told Harvard we were taking a semester off, then another semester, then a year. After that, it was pretty clear we weren’t going back.