Start with a cage containing five apes.
In the cage, hang a banana on a string and put stairs under it. Before long, an ape will go to the stairs and start to climb towards the Banana, but as soon as he touches the stairs, spray all of the apes with cold water. After a while, another ape makes an attempt with the same result -- all the apes are sprayed with cold water.
Turn off the cold water.
If, later, another ape tries to climb the stairs, the other apes will try to prevent it even though no water sprays them.
Now, remove one ape from the cage and replace it with a new one.
The New ape sees the banana and wants to climb the stairs. To his horror, all of the other apes 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 apes 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.
Again, replace a third original ape with a new one.
The new one makes it to the stairs and is attacked as well. Two of the four apes 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 ape.
After replacing the fourth and fifth original apes, all the apes which have been sprayed with cold water have been replaced.
Nevertheless, no ape ever again approaches the stairs.
"Because that's the way it's always been around here."