Stare at a fixed point long enough and the unchanging stuff around it disappears

If you fix your gaze on one spot and keep it perfectly still, objects at the edges of your vision that aren't moving or changing can fade from awareness entirely, even though they're still there. Swiss physician Ignaz Paul Vital Troxler first described this in 1804. It happens because neurons adapt to unchanging input; your visual system is tuned to notice change, not to maintain a picture of something that never varies.

— Ignaz Paul Vital Troxler, On the Disappearance of Given Objects from Our Visual Field — 1804