How does the monkey’s paw influence the characters of Mr. and Mrs. White?

Mr and Mrs White see the monkey's paw as a way to get something good for no cost.  They joke about getting the money to pay off the mortgage; only too late do they realize that the money comes at the cost of their son's life.  And then, without thinking, she wiwshes her son alive; Mr. White realizes that the "son" who will return is the mangled son who was caught in the machinery.  The fakir's prophecy is proven when they cannot control their fate.