What is the theme of “The Monkey’s Paw” ?

The theme of "The Monkey's Paw" is one with which most of us are familiar: be careful what you wish for; you might just get it. The characters in the story get their wishes granted, but in rather unpleasant, disturbing circumstances. Mr. White makes the first wish: he wishes for £200. He does indeed receive that very amount. Unfortunately, the money is in the form of compensation for the death of his son in an industrial accident.
A distraught Mrs. White urges her husband to use the monkey's paw to make a second wish, this time to bring their son back from the dead. They make a wish and hope that their son, Herbert, will soon turn up at their door. But on that fateful night, as the knocking on the door becomes louder and more insistent, Mr. White realizes that this won't be the Herbert they knew and loved; the man hammering at the door will be little more than a walking corpse in an advanced stage of decomposition. Mr. White then uses the monkey's paw once more to make his third and final wish. And when the Whites finally open the door, there is no one there.
Most people at some time in their lives love to imagine what it would be like to be granted three wishes. "The Monkey's Paw" shows us that if we want our wishes to come true, we have to make them happen instead of leaving everything to chance.