Five Monkeys were put in a large cage with a flight of steps, on the top of which was a banana. Soon a Monkey saw the banana and began up the steps to get it. All the Monkeys were sprayed with water. This stopped that Monkey and upset all the other Monkeys as well. Every time any Monkey attempted to climb the stairs to get the banana, all the Monkeys were sprayed with water. Before long, if one of them tried to climb the stairs, all the others would attack him and stop him. At this point, water spraying was no longer necessary.

Then one of the Monkeys was replaced with a new Monkey who had no experience of stairs, the banana or water spraying. Very soon the new Monkey saw the banana and headed for it. The other four Monkeys attacked him and stopped him. After a few more tries, he gave up. Then a second one of the original Monkeys was replaced with a new one. When he noticed the banana, he too jumped onto the steps to get it, and was attacked by the others. The first new Monkey joined in the attack on the second new Monkey enthusiastically.

Then a third Monkey was replaced, and, when he attempted the stairs for the banana, all the others attacked him until the third Monkey no longer made any such attempt. The same thing happened when the fourth Monkey and then the fifth Monkey were in turn replaced. Now there were five new Monkeys preventing each other from climbing the stairs, completely accepting that none of them may climb the stairs or have the banana. Even though not one of them had any idea why.