From Aesop's Fables :The Goose that Laid the Golden Eggs

A man and his wife had a goose which laid a golden egg everyday. They began to think how to get rich faster. So they imagined that the bird inside must be made of gold. They decided to kill it to get the gold. But when they cut it open it was just like any other goose. No gold inside. They did not get rich instead they lost what they had before.