THE GREEDY DOG

A hungry dog was crossing a bridge over a stream with a piece of flesh in his mouth.

Eventually he saw his own shadow in the water and took it for another Dog, with a piece of meat which double  his own when compared in size. He immediately let go of his own, and fiercely attacked the other Dog to get his larger piece from him. He thus lost both: that which he grasped at in the water, because it was a shadow; and his own, because it was flushed away with the moving water.
Moral

He who is not contented with what he has, would not be contented with what he would like to have