I went through basic training in open-floor barracks with a few folk who insisted they were 'night owls' and would play their music to 01:00 or later, falling asleep to the noise.

Initially the rest of us endured it and would turn-off the radio when they fell asleep, to then enjoy four hours sleep. After the second week, however, we managed to 'cure' the night owls.

I am sure many people suffer a medical condition that impairs sleeping. Most, however, do not.