A tub full of milk
Once there was a king who wanted to test the honesty and generosity of his courtiers. He arranged for a large tub to be placed in the palace grounds. The king then instructed each of his courtiers to bring a jar of unadulterated cow’s milk during the night and pour it into the tub, to be donated to poor people the next day.
One by one his courtiers prepared to do the task that night. In the morning, the king inspected the tub and to his surprise it was filled completely with water! There wasn’t a drop of milk in the tub!!
Each of his courtiers had thought the others would bring milk, and that he could just make do with some water and assumed that he would not be caught being dishonest because it was dark. So all of them went in succession and poured their jug of water in the tub and returned home.