We believe SpaceX will become the world leader in space transport, and we want our investors to be part of that future.

We had a mission at PayPal - which was to create a new financial system, a new world currency, and we failed. We were a financial success, but we didn't succeed at the purpose of our company.

Halcyon people have put aside and left their homes, their million dollar salaries, full professorships at major universities, and fully seed-funded startup companies to be part of this effort.

I have realised more and more that great companies, founded for a long-term purpose, such as Google or Facebook or SpaceX, may do more good in the world than any other vehicle that we have.

And that means that no matter how we reform health care, we will keep this promise to the American people: If you like your doctor, you will be able to keep your doctor, period. If you like your health care plan, you'll be able to keep your health care plan, period. No one will take it away, no matter what.

My own theory is that we are in the middle of a dramatic and broad technological and economic shift in which software companies are poised to take over large swathes of the economy.

I learned how to cook, began reading books on food. I began to understand about nutrition. It never had occurred to me that what you ate could affect how you felt. It could affect your health. It seems obvious now, but at age 23 or 22 or whatever I was, it wasn't obvious at all.

It's a pretty amazing feeling to know that something I posted on the Internet can impact so many people.