Focusing on the customer makes a company more resilient.

If you don't understand the details of your business you are going to fail.

We've done price elasticity studies, and the answer is always that we should raise prices. We don't do that, because we believe -- and we have to take this as an article of faith -- that by keeping our prices very, very low, we earn trust with customers over time, and that that actually does maximize free cash flow over the long term.

If you look at academic studies, you can see that stock prices are most closely correlated with cash flow. It's such a straightforward number. Cash flow is what will drive shareholder returns.

If you're not stubborn, you'll give up on experiments too soon. And if you're not flexible, you'll pound your head against the wall and you won't see a different solution to a problem you're trying to solve.

It’s very important for entrepreneurs to be realistic. So if you believe on that first day while you’re writing the business plan that there’s a 70 percent chance that the whole thing will fail, then that kind of relieves the pressure of self-doubt.

In the end, we are our choices.