Yesterday, Facebook founder and CEO Mark Zuckerberg took the stage at Y Combinator’s Startup School in a candid interview with Y Combinator Partner Jessica Livingston. You can watch the full interview here, and it starts around the 43 minute mark, and lasts for roughly 40 minutes. If you have some time to spare, it’s well worth a look.

Zuck revealed a number of fascinating things about entrepreneurship, founding Facebook, and product development, but one of the more interesting (and surprising points) came at the end of the interview when Livingston asked him what he would do different if he could go back in time. Zuck replied: If I were starting now I would do things very differently. I didn’t know anything. In Silicon Valley, you get this feeling that you have to be out here. But it’s not the only place to be. If I were starting now, I would have stayed in Boston. [Silicon Valley] is a little short-term focused and that bothers me.

He explained that he had a conversation once with Amazon founder and CEO Jeff Bezos about this, and the average time someone stays in job at Seattle is twice as long than it is in Silicon Valley. “There’s a culture out here where people don’t commit to doing things, I feel like a lot of companies built outside of Silicon Valley seem to be focused on a longer-term,” he explains. “You don’t have to move out here to do this.”

“There’s this culture in the Valley of starting a company before they know what they want to do. You decided you want to start a company, but you don’t know what you are passionate about yet…you need to do stuff you are passionate about. The companies that work are the ones that people really care about and have a vision for the world so do something you like.”

Zuckerberg also talked about the early days, when he was at Harvard, thinking of the idea for what would become Facebook. I was in denial that we were going to