system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why must we close our eyes in order to fall asleep?
gpt
First off; *we don't*. 

Secondly; closing our eyes prevents them from drying out during the night. There isn't a whole lot of blinking taking place during sleep, but there is certainly a lot of movement, which would dry out our eyes and potentially damage them. 

Lastly; humans naturally sleep during the night due to the reduction in light, which makes it difficult and dangerous to hunt or gather food. Closing our eyes can help to simulate the darkness of night, so that we can sleep more easily and more comfortably.