The fable ends with the moral, "Much wants more and loses all." One lesson from this moral is that those who have a lot tend to want more. For example, one who has billions of dollars and still wants more will never be satisfied: in other words, greed begets greed. He can keep on accumulating more money but he will never be happy. In the end, he may literally lose his money by being too aggressive or reckless with the means of achieving more wealth; or, he may be spiritually or emotionally "lost." To be in a perpetuating state of want/greed, never being satisfied, is to be lost in that state of greed. Being in such a state, one lives in selfishness and greed: to be spiritually lost.
A related lesson is that people should be satisfied and grateful for what they have. And certainly, those blessed enough to have good fortune (say, a goose that lays one golden egg a day) should appreciate that good fortune. Wanting more than is necessary is selfish. This fable is therefore also a lesson that being selfish can lead to some sort of downfall.
Of course, the moral is stated at the end of Aesop's fable of The Goose That Laid the Golden Eggs: "Those who have plenty want more and so lose all they have."
Attacus Greeb's main fault is his indolence and false pride, not his greed. He is unwilling to work to maintain the large farm that has been a profitable venture for his father. Instead, he wants to have things without earning them.
“I’m far too good to be milking cows,” he said. “I should be Lord of the Manor with servants and footmen...and heaps of silver and gold.”
Unrealistic about himself, Greeb imagines that he is deserving of a higher life without any reason. So, in addition to the theme of greed and dissatisfaction, there is also the moral that people should be grateful for the blessings that they have, and count these each day. In the beginning, Greeb owns a prosperous farm on which all he has to do is work, but he is too lazy; so, he sells off his "blessings." Soon, he has nothing left because he has been short-sighted in his indolent desire for a quick way to make money.
Much wants more and loses all.
The moral of the story Goose That Laid Golden Egg is the folly of being over greedy which leads to destruction of the source of benefits to a person. In this story the owner of the goose that lays golden egg is not satisfied with with just the golden eggs that the goose lays from time to time. He wants to get a lot more gold, a lot more quickly, and in the hope getting at once all the store of gold, that he believe, the goose has within its body, kills the goose. But he finds no gold. This way he is also deprived of the golden eggs that the goose was capable of laying in future.