Credentials are critical if you want to do something professional. If you want to become a doctor or lawyer or teacher or professor, there is a credentialing process. But there are a lot of other things where it's not clear they're that important.

The sky's the limit, I could become a doctor be a professor somewhere, be a counselor a teacher somewhere at a high school.

You become a great writer by writing.

People don't want to believe that technology is broken. Pharmaceuticals, robotics, artificial intelligence, nanotechnology - all these areas where the progress has been a lot more limited than people think. And the question is why.

If I had known how hard it would be to do something new, particularly in the payments industry, I would never have started PayPal. That's why nobody with long experience in banking had done it. You needed to be naive enough to think that new things could be done.

Don't bother starting the 10,000th restaurant in Manhattan. Find something to do that if you don't do it, it won't get done.