Physics is a good framework for thinking. ... Boil things down to their fundamental truths and reason up from there.

I think that's the single best piece of advice: constantly think about how you could be doing things better and questioning yourself.

The future of humanity is going to bifurcate in two directions: Either it's going to become multiplanetary, or it's going to remain confined to one planet and eventually there's going to be an extinction event.

Every mode of transport that we use - whether it's planes, trains, automobiles, bikes, horses - is reusable, but not rockets. So we must solve this problem in order to become a space-faring civilization.

Going from PayPal, I thought: 'Well, what are some of the other problems that are likely to most affect the future of humanity?' Not from the perspective, 'What's the best way to make money?'

I do think there is a lot of potential if you have a compelling product and people are willing to pay a premium for that. I think that is what Apple has shown. You can buy a much cheaper cell phone or laptop, but Apple's product is so much better than the alternative, and people are willing to pay that premium.

It's OK to have your eggs in one basket as long as you control what happens to that basket.