In “The Cask of Amontillado,” it is unclear what Fortunato did to the narrator. The narrator, Montresor, tells us that he plans to kill his rival, Fortunato, as revenge for insults and injuries. Montresor does not specify the nature of these alleged offenses. Poe’s intentional ambiguity leaves us readers to draw our own conclusions as to why Montresor so passionately hates Fortunato.
As he does in many of his other tales, Poe tells this story from the point of view of an unreliable narrator. It is tricky to determine what, if anything, Fortunato did to Montresor to make him angry enough to commit homicide.
We know that Montresor and Fortunato are both wine connoisseurs. Montresor tells us that Fortunato is arrogant and has an inflated ego. If we choose to believe Montresor, then given these clues, one possible explanation for Montresor’s rage is that Fortunato embarrassed him in front of other connoisseurs or challenged his wine expertise. For a sane person, this would not be reason enough to kill someone, but we are not certain of Montresor’s sanity.
It is also entirely possible that Fortunato did nothing to Montresor. When the two meet at the carnival, Fortunato is in good spirits and seems happy to see Montresor. This could be because he is intoxicated, or it could be because he does not have any ill will towards Montresor. Perhaps Montresor is simply insane, and these supposed insults and injuries were only perceived.