So given a Time Turner, I would tell my 21-year-old self that personal happiness lies in knowing that life is not a check-list of acquisition or achievement. Your qualifications, your CV, are not your life, though you will meet many people of my age and older who confuse the two. Life is difficult, and complicated, and beyond anyone’s total control, and the humility to know that will enable you to survive its vicissitudes.

I would advise them to aim high. To set their sights at a pretty tough target and don’t be too worried if you’re not successful at first. Just keep persisting and keep improving your standards, getting better and better and ultimately, you’ve got a pretty fair chance at achieving your desired goal. ... But, I do think that virtually everybody that’s born has the ability to be very competent at doing something. I think that, in itself, is worthy of aiming towards, just to be competent at doing anything you particularly wish to do.

The advice that I would give is try to find something that you like. Try to devote your energies to being very good at it. Try to achieve excellence. Don’t necessarily have as a goal success or getting prizes or whatever, but just doing very good work. And work hard. Keep working at it. Be patient. Realize that you don’t always see the benefits of what you’re doing, short-term. But in the end, the activities that I do, for example, scientific research, can be extremely rewarding. It’s really a very fascinating career.

I’d tell them, “If you believe in something, go for it, but know that when you go for it there’s a price to be paid. Be ready to pay that price and you can contribute to the welfare of society, and society will acknowledge you and respect you for it. And don’t be afraid. Don’t be afraid.”

We need to have mentors. I think I've always been pretty shameless about seeking out people much smarter and much more experienced than me from the very beginning. Michael Seibel and other people. And the more successful I got, the more leaders I started seeking out, whether it was investors, or Sheryl Sandberg at Facebook, or I got the opportunity to spend time with Warren Buffett and he became a close mentor of mine.

When we started Airbnb, no one wanted to invest. I felt like a failure so many days. It was small, it wasn't growing... A sane person probably would have quit. But we kept going through obscurity, through rejection. We couldn't raise money — but over time, it started growing.