Although you are generally not aware of it, your eyes are constantly jumping and jiggling around. These rapid movements keep the retinal image fresh since any image that remains perfectly fixed in one position on the retina will become invisible.

You have blood vessels that are on top of your retina, at the back of your eye. This weblike retinal vasculature should be seen superimposed on top of everything you look at, because it's smack in front of your photoreceptors. However, it is totally invisible to your perception. No matter how many movements your eyes make, they are never refreshing the image of these blood vessels. The strategy of ignoring the unchanging keeps the system poised to detect anything that moves or shifts or transforms. At the extreme, this is how reptile visual systems work: they can't see you if you stand still, because they only register change.

And this leads to a wild but logically sound speculation: are parts of the world invisible to us that should be obvious ? Imagine there were something like a cosmic rain that had existed your entire life. It would be completely invisible to you. If the cosmic rain suddenly stopped, we would believe that something had just appeared even though the real rain had just ended. To a wild but logically sound speculation: are parts of the world invisible to us that should be obvious ?