The moral is that greed leads to downfall. The wife's constant demands for more and more, from a cottage to being pope, show that being too greedy will never bring true satisfaction. In the end, they lose everything because of her insatiable greed.
The short story 'The Fisherman and His Wife' imparts the moral that there should be a limit to our desires. Initially, the fisherman's wife just wants a better living situation. But as she gets more, she becomes even more greedy. This greed blinds her to the fact that they were already better off than before. Eventually, their greed causes them to return to their original state of poverty. It's a cautionary tale about how too much greed can make us lose all the good things we already have.
Well, the moral in 'The Fisherman and His Wife' is about the perils of excessive ambition. The fisherman's wife starts with simple requests but her desires keep growing out of control. It shows that we should be content with what we have and not let our wants spiral into unending greed, or else we may end up with less than we started, just like the fisherman and his wife do.