The gorilla half of people never see

In 1999, two Harvard psychologists, Daniel Simons and Christopher Chabris, filmed a group of people passing basketballs around. They asked viewers to count the passes made by the team in white. A simple task.

Halfway through the video, someone in a gorilla suit walks in, stops in the centre, beats their chest and strolls off. They're on screen for nine seconds. And yet: around half of the viewers, busy counting, never see them. When shown the replay, they can't believe it.

The phenomenon is called inattentional blindness: when we focus on something intensely, the brain discards everything else, however obvious. It's not that you don't look; it's that looking isn't the same as seeing.

That's why phones and steering wheels don't mix: your eyes are on the road, but your attention can be somewhere else entirely.