"The Monkey's Paw" is rare in that Jacobs essentially states the theme in the text. Sergeant-Major Morris tells the Whites that "fate ruled people's lives, and that those who interfered with it did so to their sorrow." This is Jacobs' direct theme: that one cannot control his/her fate, no matter how hard one tries to manipulate it.
One clear example is the White family's first wish. Mr. White wishes for 200 pounds: an attempt to change their fate. They think they're being reserved and rational by not asking for more, but the result of the wish shows that they have failed to change their destiny. They do indeed get their 200 pounds, but at a price they would never be willing to pay.
A second example is, of course, the climax of the story. The tension-filled moments before Mrs. White opens the door on nothingness are particularly powerful. Although the Whites have used their second wish to have their son back, Mr. White realizes just in time that they are attempting to control something that cannot be controlled. Thus, his last wish returns their lives to the path that destiny has chosen for them, not necessarily the one they would want themselves.
"The Monkey's Paw" is a rare story in that the theme is actually stated in the story. Sgt. Maj. Morris tells the Whites that the old fakir who put the spell on the paw said, "Fate rules people's lives and those who interfere with fate do so to their sorrow." The message is a warning, but Mr. White doesn't believe it. Even though Sgt. Maj. Morris makes it clear that he tried wishing with unfortunate results and he tries to throw the paw on the fire, Mr. White makes a wish for 200 pounds only to find that he receives the money when Herbert dies in a factory accident. According to the fakir, then, because Mr. White had wished for something he should not have had, his son lost his life.
The second wish that Mrs. White encourages him to make is for Herbert's return--one week after his death. When the strange knocking begins at the door during the windy night, Mr. White panicks, believing that the previously dead but still mangled Herbert could have walked home from the cemetary and is now at the door. Because he fears what his wife will find if she opens the door, Mr. White makes his third wish--for the noise to stop.
Therefore, he uses his three wishes and to his sorrow, loses his son and disappoints his wife, who fervently believed that their son was at the door. She wanted him back, regardless of his condition.