Same here. Any time you are working a difficult problem, especially one that is difficult because of its complexity, you have to keep a lot of context in your head. In that situation, keep going as long as you can and are still making progress. This is the same problem, but in a more extreme context, as the "getting back on track" problem caused by interruptions that was discussed in Peopleware, and frequently since.
There was a discussion program on radio here in Finland (Eftersnack on YLE Vega) where they talked about heavy jobs and one job, along the other works job that contained physical challenge, was the job as a software engineer. They compared it to playing chess all day long; "the next move is yours and you cannot get it out of your head, you think about the move (read problem in your code/application) all day and night long". Although they went a little bit over the top with the comparison they still hit the nail.
