I can work 10 hours a day and be quite productive. I don’t do it on a regular basis but when things get tough I can keep a schedule like that for weeks. Difference is though that I work from home. So I don’t spend time on various trivialities and I split my 10-hour work in two parts with a nice two hour nap in between. Also I’m an early riser. Starting my day at 5:30, by midday I've accumulated 6 hours of very productive work. I won't argue that working long hours is the smartest thing anyone can do but it's nice to know an effective way to do it if the need arises.