It's good to have a fear of heights. I mean, it's kind of crazy not to because if you just lean out a little bit and there's a gust of wind or somebody bumps you or something and you fall, you're splat.

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.

You can't just ignore spacewalking suit; it partially defines the experience. So maybe the most difficult thing is becoming completely attuned to efficiently wearing a garment that is so inhibiting to motion, and making it look effortless, as if it's the most natural thing to be out there on a spacewalk.

Almost everything worthwhile carries with it some sort of risk, whether it's starting a new business, whether it's leaving home, whether it's getting married, or whether it's flying in space.

Competence means keeping your head in a crisis, sticking with a task even when it seems hopeless, and improvising good solutions to tough problems when every second counts. It encompasses ingenuity, determination and being prepared for anything.

Other anatomical changes associated with long-duration space flight are definitely negative: the immune system weakens, the heart shrinks because it doesn't have to strain against gravity, eyesight tends to degrade, sometimes markedly (no one's exactly sure why yet). The spine lengthens as the little sacs of fluid between the vertebrae expand, and bone mass decreases as the body sheds calcium. Without gravity, we don't need muscle and bone mass to support our own weight, which is what makes life in space so much fun but also so inherently bad for the human body, long-term.

Almost everything worthwhile carries with it some sort of risk.