What can happen when you are not contented with what you have and want more (it all)...

Fable: The Goose That Laid the Golden Egg
In words - http://www.storyit.com/Classics/Stories/goldengooseegg.htm
Video - http://www.youtube.com/watch?v=7dMBKgSlUPg

'To kill the Goose That Laid the Golden Eggs' is an idiom used of an unprofitable action motivated by greed.

"Be thankful for what you have; you'll end up having more. If you concentrate on what you don't have, you will never, ever have enough."
- Oprah Winfrey

"You say, 'If I had a little more, I should be very satisfied.' You make a mistake. If you are not content with what you have, you would not be satisfied if it were doubled."
- Charles H. Spurgeon