There was a cage with several apes in it.
In the cage there was a banana hung on a string, and stairs under it.
Before long an ape went to the stairs to get the banana, but as soon as it even touched the stairs, all apes were sprayed with water. After a while the same ape or another one made another attempt, with the same result: all apes are sprayed. If later another ape tries to climb the stairs, the others will try to prevent it.

Now they took one ape from the cage and put in a new one. The new ape saw the banana, and wanted to climb the stairs. To his horror all other apes attacked him. After another attempt he knew: if he wanted to climb the stairs, he would be beaten up. Then they removed a second ape and replaced it by another new one. The newcomer went to the stairs and got beaten up. The previous new ape took part in the punishment with enthusiasm.

A third old ape was replaced by a third new one. The new one made it to the stairs and got beaten up as well. Two of the apes who beat him have no idea why they may not climb the stairs. They replace the fourth old ape, and the fifth, etc. until all apes which have been sprayed with water have been replaced.

Nevertheless, no ape ever tries to climb the stairs.

One day a new, young ape asks, "But Sir, why not?"
"Because that's the way we do things around here, my boy."