Inspired by Terry Tao's career advice page and by a recent interview on Math-Life balance, I collected here some thoughts on productivity in math. The recent interview was with Saul Glasman and in it he mentioned, more as a side note, that math research is hard because one often gets stuck while working on a problem. It's just very hard to focus for a long time on a single problem, seemingly without any progress. But the crucial insight here is, in my opinion, the fact that it only seems as if there is no progress.
According to Glasman, when it happens that you work too long on a problem and then take a break, you can't really get yourself to work on it again and start feeling bad because you think you must work on that one problem until there is a breakthrough. This leads to a downward spiral because you think that it is your job to work on or solve this problem and you can't even get yourself to do your job. But this is probably false and Terry Tao knew this for a long time.