Multiple tales in Poe’s Stories are told via flashback. Poe’s use of flashback in stories like “The Pit and the Pendulum,” “The Tell-Tale Heart,” and “The Cask of Amontillado” is essential in building the tense atmosphere that characterizes so much of his work.
Written in the past tense and frequently featuring narrators who seek to avail themselves of guilt or profess their sanity (thereby counterintuitively demonstrating their insanity), these stories are particularly tragic because they are already over before they’ve begun—there is no opportunity for change, growth, or redemption. The nameless narrators seek to unburden themselves, but no matter the justifications offered, the reader knows that a terrible ending is about to unfold.
In the case of “The Cask of Amontillado,” the narrator is 50 years too late in his confession. He admits this in the following passage:
I forced the last stone into its position; I plastered it up. Against the new masonry I re-erected the old rampart of bones. For the half of a century no mortal has disturbed them. In pace requiescat!
The narrator’s final sentence in Latin translates to: “Rest in peace!” The fact that the narrator concludes his flashback about his revenge plot by making such a declaration 50 years after the fact solidifies the horror and tragedy of what he has done. And this, in turn, short-circuits any kind of remorse he might otherwise show about what he has done—regardless of how he feels, what's done is done.