system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How come when you close both eyes you see black but when you close one eye you just see nothing?

Why don’t you see black on that one eye when you close it?
gpt
Your brain is a very sophisticated computer. You’ll notice you actually can see red through your closed eyelids, if you look at the lights. 

What happens is your brain filters out the one eye that’s seeing all red as unnecessary information and only utilizes the eye that can see a full picture.

Try closing one eye and holding your hand over the other, but far enough that you can see light leaking around the edges. You’ll notice the eye you closed is actually “visible” now as a reddish blob.

Our brains are really good at filtering out constant signals like the hum of machines or say the tick-tock of a clock. We only notice changes to our environment, and with a closed eye there is no change to notice. It’s kinda like how your nose is in your field of vision but you don’t notice it 99.9% of the time.