I actually believe with some further research, we could find the neuroscience research support that tells us that it's a brain design issue related to energy consumption and utilization - it's why Pomodoro method works so surprisingly well. I'm thinking about Dr. White's book, "Why We Sleep" and his research about how the brain's energy utilization builds up plaque that gets "cleaned up" at night when we sleep -- similar to how oil gets dirty as the car's engine runs. Maybe not the best analogy, but okay for now.