An experiment was run at Harvard University that has been repeated frequently since. Spectators at a basketball game were asked to maintain a count of the number of successful passes one of the teams made. In the middle of the game, a person dressed in a gorilla suit ran on to the court, stood in the middle, beat their chest, then ran off. When spectators were asked if anything unusual had occurred during the game, half of them had not seen the gorilla. When they were shown the video, some of them claimed that the video must have been doctored. This phenomenon is known as “inattentional blindness” – when you are focusing hard on something (here, counting the number of passes), you can completely miss a dramatic event occurring before your eyes.
On the night of 29th December 1972, Eastern Air Lines flight 401 flew from JFK airport, New York, to Miami. As it came in to land, the undercarriage was lowered but the light confirming the nose-wheel was locked did not come on, so the pilot requested to circle while they sorted out the problem. They put the plane on auto-pilot and both the pilot and co-pilot focused on the light. They removed it, blew the dust off it, stuck it back in, but in the meantime, they had inadvertently disengaged the auto-pilot. The plane was losing height fast, the altitude alarm sounded and the altimeter showed rapid loss of height, but the pilot and co-pilot neither heard the alarm (which can be clearly heard on the black-box recording) nor saw the altimeter dial dropping fast, despite being within their line of sight. One of the last things heard on the recording is the co-pilot saying “we’re still at 2,000 feet, right?”. Seconds later, the plane crashed into the Everglades, killing 101 people. The light bulb was faulty and the nose wheel was correctly in position. The plane crashed as a result of the failure of a $12 light bulb.
Flight crew training has since been adapted to ensure that pilot and co-pilot duties are segregated.
Focusing on one risk can mean that you become blind to other risks that may require attention before they do you serious harm.
Source: “The Luck Factor” – Richard Wiseman, “Bounce” – Matthew Syed, Wikipedia