The Dog and the Bone - Aesop fables

It so happened that a dog had a fine bone and was carrying it home to chew on in peace.

On his way, he had to go across a plank over a stream.

As he walked across the plank, he looked down and saw his reflection in the water.

Thinking that it was another dog with another bone, he made up his mind to have that bone, too.
 
But when he snapped at his reflection, his own bone fell into the water and was lost forever.

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The greedy often lose what they have.