"The Cask of Amontillado" by Edgar Allan Poe was Poe's last short story. It is certainly a masterpiece of horror. The grotesque settiing and madness of the main characters lead the reader into revenge, murder, trickery, and betrayal.
The narrator of the story is the main character or unsympathetic, protagonist Montresor. He is not the normal, heroic main character. The force that drives Montresor is his need to punish Fortunato with impunity. In translation, Poe meant that Montresor wants to commit the perfect crime; and that is exactly what he does. The reader learns at the end of the story that Montresor has told the story as a flashback fifty years later.
Back in the time of this story, when someone insulted another person, often the problem would be resolved with a duel using some kind of swords. This is is not how Montresor wishes to acquire his vengenance.
Why does Montresor seek revenge? Fortunato has injured him not physically but verbally or spiritually many times. The thing that sends Montresor over the edge was an insult that Fortunate inflicted on him. Most people do not kill because they have been insulted:
The thousand injuries of Fortunato I had borne as I best could, but when he ventured upon insult I vowed revenge. You, who so well know the nature of my soul, will not suppose, however, that I gave utterance to a threat.
Apparently, to Poe, the details of the insults or injuries were not important. It was how the insult was repaid that became the crux of the story. This is taking the old cliche in reverse to the fartherest limit: Sticks and stones may break my bones, but words will never hurt me. In this story, this is not the case.
Poe allows some insight into the thinking of Montresor when he gives the family motto and coat of arms. Apparently, if something is done to this family, there will be revenge. The snake being stepped on and turning back and biting the foot indicates there will be vindication.
The story circulates around the trickery, betrayal, and trust held between these two characters. Fortunato trusts Montresor enough to follow him down into the catacombs to taste wine. Then, Montresor feels betrayal by a supposed friend who has insulted that friendship; therefore, he will use a ruse to get his arrogant, drunken "friend" to follow him all the way to his death.
Poe opens his story with the following two sentences:
THE THOUSAND INJURIES of Fortunato I had borne as I best could, but when he ventured upon insult I vowed revenge. You, who so well know the nature of my soul, will not suppose, however, that I gave utterance to a threat.
Poe is using the fiction that his protagonist Montresor is addressing someone who knows him intimately. It seems likely that this narrative was supposedly contained in a hand-written manuscript which somehow came into the hands of an American writer/editor who translated it from Italian (or possibly French) and published it in a ladies' magazine. By creating this fiction and this fictitious confidante, Poe relieves himself of the need to explain many things and focus on what is dramatic. Montresor should not have to give examples of the "thousand injuries" because he must have told his correspondent about a lot of them already. The single insult Montresor refers to is not sufficiently important to describe. It is the thousand injuries which Montresor has borne that will lead to Fortunato's death; the one insult only shows that Fortunato is escalating his abuse because he has been led to believe that Montresor will tolerate it.
Why should Montresor put up with a thousand injuries? These must have occurred over a period of years. Why didn't he just break off relations with Fortunato? Ir must be that he is financially dependent on this insolent man. The third paragraph of the narrative suggests that they are both gentlemen-businessmen who deal in expensive merchandise such as oil paintings, antique furniture, jewelry (gemmary), and no doubt in gourmet wines. Fortunato is rich and Montresor is poor. No doubt Montresor receives part of his income through his relationship with Fortunato. For example, Montresor might receive finders fees on transactions which he cannot afford to handle himself. Venice is a dying city in which many impecunious aristocrats are surviving in their dilapidated palazzi by selling off priceless heirlooms which might include masterpieces by Renaissance artists. Naturally the sellers would want respect, secrecy, and reliability. Since Montresor appears to know more about some luxury goods than Fortunato, the two men could have a symbiotic relationship, although Fortunato would always have the upper hand because he was the one with the most capital. He also appears to have a much older name and an insider status in Venetian society.
Poe avoided describing any of Fortunato's injuries because, in addition to making his story longer, it would have been hard to think of injuries that would not have become generally known. If people thought Montresor had been seriously and repeatedly injured, then Montresor would become a prime suspect when Fortunato disappeared--and Montresor wants to be absolutely above suspicion.
Poe deliberately requires his reader to make guesses. This is a good way to involve a reader in a story. Ernest Hemingway did something similar in some of his best short stories, including "The Killers" and "Hills Like White Elephants"--but Poe did it long before Hemingway.