Curiously the book Why We Sleep says the exact opposite: we all have natural sleep cycles that differ and it's genetic, impossible to change. What I've noticed

Curiously the book Why We Sleep says the exact opposite: we all have natural sleep cycles that differ and it's genetic, impossible to change. What I've noticed is that it's possible to keep a consistent schedule and overcome all of that inertia, but if you slip up you'll find yourself back in your natural cycle. Interestingly, the cited reason for this is that evolutionary, it's an advantage to not have everyone asleep at the same time.