Start with a cage containing five monkeys.

Inside the cage, hang a banana on a string and place a ladder under it. Before long, one of the monkeys will spot the banana and start to climb the ladder. As soon as he does, spray all of the other monkeys with cold water.

Replace the banana.

After a while another of the monkeys will probably go for the banana. Again, spray all of the other monkeys with cold water. Monkeys are fairly smart, so pretty soon whenever one of the monkeys tries to climb the ladder all the other monkeys will try and prevent him doing it. When this happens, put away the cold water. Remove one monkey from the cage and replace it with a new one. Then put another banana at the top of the ladder.

The new monkey will spot the banana and make for the ladder. To his surprise all of the other monkeys attack him. After a couple more attempts result in further beatings the new monkey will not make any attempt to go for the banana.

Remove another of the original monkeys and replace it with another new one. Then replace the banana. Again, the new monkey will make a grab for it. Like his predecessor he will be amazed to find that all the other monkeys attack him. The previous newcomer will take part in his punishment with some enthusiasm.

One at a time, gradually replace all of the original monkeys with new ones. Each of the newcomers will go for the banana. Each one will be attacked by the other four. Most of the new monkeys have absolutely no idea why they were not allowed to climb the ladder, or why they are participating in the assault on the newest monkey.

When all of the original monkeys have been replaced, none of the remaining monkeys have ever been sprayed with cold water. Nevertheless no monkey ever approaches the ladder. Why not? Because as far as they are concerned that's the way it has always been done around here.