Yesterday, I came across something called motion-induced blindness.
You can experience it yourself by staring at the blinking green dot in the middle of the image below.
(image created by Mlechowicz, from Wikipedia Commons;
Michael Bach has an interactive example of this and
lots of other illusions as well)
What should happen, and what happens to me, is that some or all of the yellow dots will randomly disappear from sight.
They will be gone.
The wikipedia article says that "The illusion catches the brain ignoring or discarding information," and suggests that we don't really know why our brain does this.
The example above is a case of our brain intermittently hiding something from us. But the startling effectiveness of this hiding makes me wonder: what else out there in reality is our brain always hiding from us?