Why does Montresor vow revenge on Fortunato in "The Cask of Amontillado" by Edgar Allan Poe?

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chilling short story "" is a tale of retribution. In the outset, the first person
narrator Montresor vows revenge against his supposed friend Fortunato over some
"insult." The affront, which must have been significant, is never revealed. It is,
however, egregious enough for Montresor to devise a devious and horrible plan to lure Fortunato
into the catacombs below his estate with the pretense that he wishes to have Fortunato's opinion
about a bottle of rare wine. While in the underground chamber, Montresor chains Fortunato to the
catacomb and proceeds to wall him in with brick and mortar. There are two important elements to
Montresor's plan. First, it must be well known to Fortunato that Montresor is the one bringing
about his demise. Second, Montresor sets up his plan so he will never be apprehended for the
crime. Fortunato simply disappears. Some critics believe Montresor is telling his story to a
priest at the end of his life, revealing a certain amount of remorse on Montresor's part.
Whatever the reality, the reader is never made aware of the exact motive which prompted
Montresor to kill Fortunato in such a ghastly way.