I often like to point out that we are completely blind to the most common thing around us, nitrogen gas. This blindness is good, because it allows us to attend to everything else, instead of stumbling around through a fog and over cliffs and into the maws of ambush predators.

While it's usually part of a rant about false color pictures in astronomy, it applies cognitively too. It's about the signal to noise ratio, and what constitutes signal versus noise can change in an instant.