Much like his advice about getting hired, this is some fantastic advice about building a product people want to use:

If you started your project without talking to a single soul you’re doing it wrong. If you’ve talked to 100 people, it won’t matter until you connect with a group of people who need your help. That’s where you start. Not with yourself, and your ideas, but with other people.

By the same token, if you ever have a moment where you don’t have any ideas on something to build it’s because you’re not talking to people. Everyone has problems they need solved. I know for myself, it’s easy to just settle in at night to hack on a side project simply to play with a new technology. That’s fine, but technology does not make a product.