Work While Alert

I recently came across a graph showing the levels of alertness of working people between the ages of 18-65. (Teenagers seem to have a distinctively different sleeping pattern.) It shows, that on average, we are the most awake at around noon, three o'clock in the afternoon and during the early hours of the evening. How come we take breaks during the periods we are most alert? As a high achiever schedule your working hours for the times you are the most alert.