For me, the big shock has always been the extent to which sleep can kill a fantastic streak of productivity. I sometimes have weeks of incredible energy, where I work 12 or even 14 hours every day, and I do my best work, and I have deep insights, and invent new products and new kinds of software. And generally, over the course of a week or two, I become more productive each day. And finally I have a day when I am on fire and I'm writing incredible code and I'm writing some of my most popular essays, the stuff that continues to be read years later. And I go to sleep thinking that tomorrow will be just as good. And I sleep 9 hours. And I wake up and I am a completely different person. My thoughts don't make sense. I'm a bit disoriented. I drink 3 cups of coffee but I still feel groggy. I have no energy. The magic is gone. I'm lucky if I get 4 hours of good work done. And the next day is terrible, and the next day is terrible, and the so on. And it is always a shock what a sudden start there is to this prolonged grogginess, and it always seems to start with one night where I sleep a bit too long.