> [W]hen I am totally engrossed in solving a problem, I get into a flow and the time flies by. If the problem is both interesting and challenging, I can't wait

> [W]hen I am totally engrossed in solving a problem, I get into a flow and the time flies by. If the problem is both interesting and challenging, I can't wait to get back to working on it and I hate having to stop! I agree that it is possible to remain in a state of flow for "the standard industrial eight", but on occasions where I've remained in a state of flow for eight (or more) hours, the quality of the work suffers, and the following day is a total loss (as in "me no think good, think meat broken"), so it is better to keep to a more sustainable pace.