This is the big question that will never be answered. Mr. White made his third wish when somebody was pounding on the front door. He wished for that person to go away forever, and
The knocking ceased suddenly, although the echoes of it were still in the house. He heard the chair drawn back, and the door opened. A cold wind rushed up the staircase, and a long loud wail of disappointment and misery from his wife gave him courage to run down to her side, and then to the gate beyond. The street lamp flickering opposite shone on a quiet and deserted road.
Mrs. White assumed it was their son Herbert. Mr. White was afraid she was correct. But it could have been a sheer coincidence that some other person happened to knock on their door shortly after Mr. White, on his wife's insistence, wished that Herbert would come back to them. The reader also imagines that it is Herbert outside and is afraid, like Herbert's father, of what the son will look like when the door opens. He was torn up by the machinery at the plant where he worked, and he has been in the grave for a long time. He could be a horrible monster. His behavior might be nothing like his funny, cheerful self in Part I.
The only conceivable alternative explanation for the knocking is that someone was lost out there in that remote, unpopulated area and was trying to get directions. That person would have known that there were people inside the Whites' little house because he would have seen the light in the bedroom window.
He sat until he was chilled with the cold, glancing occasionally at the figure of the old woman peering through the window. The candle-end, which had burned below the rim of the china candlestick, was throwing pulsating shadows on the ceiling and walls, until, with a flicker larger than the rest, it expired.
So it could have just been a coincidence. Early in Part II, Mr. White tells Herbert:
"Morris said the things happened so naturally," said his father, "that you might if you so wished attribute it to coincidence."
If the granting of wishes seemed like coincidences, then it would appear that Herbert was doomed to be killed at the manufacturing plant regardless of whether his father had wished for two hundred pounds or not. Herbert stayed up late the night before and undoubtedly drank more whiskey than he was accustomed to drinking. Sergeant-Major Morris stayed late, and the family stayed up still later talking about the monkey's paw. Mr. White made his first wish that very night. When Herbert went to work he had had less sleep than usual and was hung over from the whiskey. That could explain why he was less attentive and got caught in the machinery. If Mr. White had not wished for two hundred pounds, then, he would still lose his son.
"The Monkey's Paw" is like another classic short story, "The Lady or the Tiger?" No one will ever know if the princess's lover married her beautiful rival or whether he got killed and eaten by the tiger. And no one will ever know if Herbert really came back to life as a result of Mr. White's second wish.