Classicly

Many a man will tell you that he does his best work in the wee watches of the morning, after tedious hours of persevering but fruitless effort. Instead of being exhausted by its long hours of persistent endeavor, the mind seems now to rise to the acme of its power, to achieve its supreme accomplishments.

Difficulties melt into thin air, profound problems find easy solution. Flights of genius manifest themselves. Yet long before midnight such a one had perhaps felt himself yield to fatigue and had tied a wet towel around his head or had taken stimulants to keep himself awake.