system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it so easy to stay up later, but so difficult to go to sleep earlier?
gpt
Being able to force yourself to stay awake is an evolutionary advantage, so we have many ways to keep ourselves awake. Stimulating any of your senses will keep you awake, since you never know if that twig snapping or that scent or that shadow is a predator hunting you. It's beneficial to your survival to remain awake. Falling asleep is necessary, obviously, so it's designed to take over when there are no other stimuli keeping you awake.

In essence, there are nearly infinite conditions that will keep your body awake, but only a few conditions where you will sleep.