Constantly seek criticism. A well thought out critique of what you're doing is as valuable as gold

I think that's an important thing to do, to really pay attention to negative feedback, and solicit it, particularly from friends. This may sound like simple advice, but hardly anyone does that, and it's incredibly helpful.

The lessons of history would suggest that civilisations move in cycles. You can track that back quite far - the Babylonians, the Sumerians, followed by the Egyptians, the Romans, China. We're obviously in a very upward cycle right now and hopefully that remains the case. But it may not.

The problem is that at a lot of big companies, process becomes a substitute for thinking. You're encouraged to behave like a little gear in a complex machine. Frankly, it allows you to keep people who aren't that smart, who aren't that creative.

What most people know but don't realize they know is that the world is almost entirely solar-powered already. If the sun wasn't there, we'd be a frozen ice ball at three degrees Kelvin, and the sun powers the entire system of precipitation. The whole ecosystem is solar-powered.

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

Starting and growing a business is as much about the innovation, drive and determination of the people who do it as it is about the product they sell.