Start with a cage containing five monkeys.
In the cage, hang a banana on a string and put stairs under it. Before long, a monkey will go to the stairs and start to climb towards the banana.
As soon as he touches the stairs, spray all of the monkeys with cold water.
After a while, another monkey will make an attempt with the same response - all of the monkeys are sprayed with cold water. Keep this up for several days.
Turn off the cold water.
If, later, another monkey tries to climb the stairs, the other monkeys will try to prevent it even though no water sprays them.
Now, remove one monkey from the cage and replace it with a new one.
The new monkey sees the banana and wants to climb the stairs. To his horror, all of the other monkeys attack him. After another attempt and attack, he knows that if he tries to climb the stairs, he will be assaulted.
Next, remove another of the original five monkeys and replace it with a new one. The newcomer goes to the stairs and is attacked. The previous newcomer takes part in the punishment with enthusiasm.
Replace the third original monkey with a new one. The new one makes it to the stairs and is attacked as well. Two of the four monkeys that beat him have no idea why they were not permitted to climb the stairs, or why they are participating in the beating of the newest monkey.
After replacing the fourth and fifth original monkeys, all the monkeys which have been sprayed with cold water have been replaced. Nevertheless, no monkey ever again approaches the stairs.
Why not? Because that's the way it's always been done around here.