You can miss a change happening in front of you

If a change coincides with a brief interruption — a flicker, a blink, a cut — people often fail to see it, even when it is large.

In the flicker paradigm, two versions of a photograph alternate with a brief blank between them. A jet engine appears and disappears, a building jumps, and observers take seconds to find it. In the real world, Daniel Simons and Daniel Levin had a stranger ask for directions and, during a moment when a door passed between them, swapped the stranger for someone else. About half the subjects did not notice.

Once the change is pointed out it is obvious, which is why the failure feels like a trick. It is a limit of attention, not of the retina. The image was there. The comparison was not made. Driving, aviation, and eyewitness work all have versions of the same gap.