I don't think you're alone in this. That seems to be about my limit as well. If one is focusing as hard as they possibly can on a complex problem, I think the l

I don't think you're alone in this. That seems to be about my limit as well. If one is focusing as hard as they possibly can on a complex problem, I think the limit is more like 25 hours a week. I have been wondering whether there is any psychological research on this. I imagine that it would be hard to do since focus and productivity are difficult things to measure in a way that would be externally valid.