What is the universal truth in "The Monkey's Paw"?
There is more than one universal truth to "The Monkey's Paw." In fact, for a story that is so brief and cheesy, there is a surprising amount of deep and yes, universal truth to the story.
The first is a cautionary truth: if something seems too good to be true, it is. When the family gets the paw, which has the ability to grant wishes, it really can grant wishes...but at a terrible cost. They get the 200 pounds the father wished for, but only because their son is killed in an industrial accident, and they get the money as compensation. That's the biggest truth, and a very bitter one.
The second universal truth is that people don't listen, or don't learn from other people's experience. The soldier told them that the man who used to own the paw had literally wished to die. That's how badly the first two wishes had distorted his life. But they took it anyway.
And a universal truth that is less profound deals with culture. People are willing to believe in magic from far away, even if they don't respect the country that it came from. (That's a minor part of the story.)