Gorilla tactics

There is a video in which a small group of students amble about passing a basketball back and forth. The instruction at the start is to count how many times the players pass the basketball. Then comes the punchline – did you see the gorilla?

Halfway through, a figure in a gorilla suit walks through the middle of the scene, beats its chest and walks off. It was designed as a psychological experiment, with the startling outcome that about half the viewers missed the gorilla altogether. One explanation is obvious – they were focused on the basketball. But how can you miss a gorilla?

Blunders at the chessboard can be just as perplexing. True, some are easily ascribed to nervousness or carelessness. Those are often the ones where you kick yourself right after making the move. But equally, one may feel an intense concentration, right before some blindingly obvious response which comes as a terrible shock.