This delusion is why there are periodic economic crashes. It sticks around because if you are powerful you can take advantage of the thinking when times are good and skip the consequences when times are bad. When too many believe it's true, they allow it to be true.

The cost? An ever increasing chasm between powerful and powerless, a chasm which itself goes through periodic crashes which tend to be significantly more violent... e.g. the fall of Rome, the French Revolution, and WWII.