How does Arthur Conan Doyle make the ending of "How It Happened" so effective?

Because the victim of the accident is also the narrator of "How
It Happened" by Arthur Conan Doyle, the reader expects merely a continuation of the narrative by
this character rather than his death. In addition, as the narrator says after the crash, "When I
became aware of my own existence once more," the reader continues to believe in the same mode of
narration that has been begun. Also, with a dialogue between this narrator and his friend,
Stanley for whom, the narrator remarks, he "had a genuine affection" (Somehow the reader probably
misses the use of the past tense, had), the reader believes that the
narrator is conscious. And, it is not until "a wave of amazement" comes over the narrator as he
realizes that Stanley has died in the Boer War, so he, too, must be dead.