The Dog and His Bone
A hound dog found a bone and held it tightly in his mouth. He growled and scowled at anyone who attempted to take it away. Off into the woods he went to bury his prize.
When he came to a stream, he trotted over the footbridge and happened to glance into the water. He saw his own reflection. Thinking it was another dog with a bigger bone, he growled and scowled at it. The reflection growled and scowled back.
"I'll get THAT bone too," thought the greedy dog, and he snapped his sharp teeth at the image in the water.
Alas, his own big bone fell with a splash, out of sight, the moment he opened his mouth to bite!
By being greedy, one risks what one already has.