Decide in your heart of hearts what really excites and challenges you, and start moving your life in that direction. Every decision you make, from what you eat to what you do with your time tonight, turns you into who you are tomorrow, and the day after that. Look at who you want to be, and start sculpting yourself into that person. You may not get exactly where you thought you'd be, but you will be doing things that suit you in a profession you believe in. Don't let life randomly kick you into the adult you don't want to become.

Early success is a terrible teacher. You're essentially being rewarded for a lack of preparation, so when you find yourself in a situation where you must prepare, you can't do it. You don't know how.

Life off Earth is in two important respects not at all unworldly: you can choose to focus on the surprises and pleasures, or the frustrations. And you can choose to appreciate the smallest scraps of experience, the everyday moments, or to value only the grandest, most stirring ones.

It's puzzling to me that so many self-help gurus urge people to visualize victory, and stop there. Some even insist that if you wish for good things long enough and hard enough, you'll get them - and, conversely, that if you focus on the negative, you actually invite bad things to happen. Why make yourself miserable worrying? Why waste time getting ready for disasters that may never happen? Anticipating problems and figuring out how to solve them is actually the opposite of worrying: it's productive. Likewise, coming up with a plan of action isn't a waste of time if it gives you peace of mind. While it's true that you may wind up getting ready for something that never happens, if the stages are at all high, it's worth it.

It's never either-or, never enjoyment versus advancement, so long as you conceive of advancement in terms of learning rather than climbing to the next rung of the professional ladder. You are getting ahead if you learn, even if you wind up staying on the same rung.

I wasn't lonely. Loneliness, I think, has very little to do with location. It's a state of mind. In the centre of every city are some of the loneliest people in the world. If anything, because our whole planet was just outside the window, I felt even more aware of and connected to the seven billion other people who call it home.

My optimism and confidence come not from feeling I'm luckier than other mortals, and they sure don't come from visualizing victory. They're the result of a lifetime spent visualizing defeat and figuring out how to prevent it. Like most astronauts, I'm pretty sure that I can deal with what life throws at me because I've thought about what to do if things go wrong, as well as right. That's the power of negative thinking.

Value the wisdom of humility, as well as the sense of perspective it gives you.

If I'd defined success very narrowly, limiting it to peak, high-visibility experiences, I would have felt very unsuccessful and unhappy during those years. Life is just a lot better if you feel you're having 10 wins a day rather than a win every 10 years or so.

Nothing boosts confidence quite like simulating a disaster, engaging with it fully, both physically and intellectually, and realising you have the ability to work the problem.