A good programmer working intensively on his own code can hold it in his mind the way a mathematician holds a problem he's working on. Mathematicians don't answer questions by working them out on paper the way schoolchildren are taught to. They do more in their heads: they try to understand a problem space well enough that they can walk around it the way you can walk around the memory of the house you grew up in. At its best programming is the same. You hold the whole program in your head, and you can manipulate it at will.

I was discussing my recent experience with programming dreams, some might say nightmares, with Cliff Hall. He pointed me to this essay from Paul Graham that really nails it. It is so difficult to just shut down after a long period of working on a difficult programming problem. I find myself staying up way to late, because I don't want my brain to lose the trail with mere sleep. Will... sleep... when... dead...