I have always noticed a significant drop in ability after about 6 hours of work and unless urgent I switch to tasks that require far less mental concentration. A good lunch, perhaps with exercise helps recover an extra hour or so at most. Almost invariably, the next morning after a sleep, problems that took considerable effort the previous day now seem clear and straight forward.<p>So HN, I'm curious how many hours a day you feel you are nearly fully effective in your work.
Could be 10 hours and more in real life. But in a work environment, 8 hours, 5 days a week I am happy for 4 productive hours a day basically wasting the other 4 plus meal time.