system
Given the following post, respond as if you're commenting on Reddit:
human
Why is it that when you're in a "dark" room and you focus on a really dark spot, everything, even light, will start to fade away?

I know I probably didn't make any sense since it's hard to explain but imagine being in a dark room with nothing but a little red LED light in the center of the room, if you focus on a dark corner you can see how this light will fade away into darkness. Why is that?
gpt
What you describe is an example of Sensory Adaptation. Through the process of sensory adaptation, our sensory systems become less sensitive to constant, unchanging stimuli. 

In your scenario, if your eyes remain motionless, what little light is present will continually stimulate the same retinal photoreceptors at the same level.  Sensory adaptation reduces our awareness of such a constant stimulus. In the case, the dim light will seem to fade.  But twitch your eyes just a bit and the perception is restored.

Your other senses exhibit similar adaptations.  You may smell a pungent aroma upon entering a room, but remain there and soon you may be entirely unaware of it.    When you wear a new wristwatch or ring, you may at first be aware of the sensation of pressure on your skin, but after a while you no longer notice it.