Caught at it or failed to have Fortunato know he is being punished. Early in the story Montresor states: " I must not only punish but punish with impunity. A wrong is unredressed when retribution overtakes its redresser. It is equally unredressed when the avenger fails to make himself felt as such to him who has done the wrong."
Montresor's revenge might not be successful if Fortunato manages to escape from the catacombs, if someone intervenes and rescues Fortunato before Montresor can exact his revenge, or if Montresor's guilt over committing the murder overwhelms him before he can achieve satisfaction from his revenge.
In the very first line of the story, Montresor says: "The thousand injuries of Fortunato I had borne as I best could, but when he ventured upon insult I vowed revenge." So the answer is Montresor vows revenge in the first line of the story, but only after Fortunato has already committed a thousand injuries but now has also insulted Montresor. This is significant because it creates some doubt as to the sanity of the narrator, Montresor. He vows revenge not after a thousand "injuries," but only when Fortunato adds insult as well. It is as if the more trivial of the two, injury and insult, has become the most important.
It is suggested in Edgar Allan Poe's story "The Cask of Amontillado" that Fortunato insulted or wronged Montresor in some way, although the specific details of the offense are not explicitly stated. This offense likely involved a significant betrayal or humiliation that fueled Montresor's desire for revenge.
Montresor traps Fortunato in the catacombs beneath his palazzo by enticing him to sample a cask of Amontillado. He takes advantage of Fortunato's arrogance and pride to lead him deeper into the underground passages, eventually chaining him to a wall and leaving him to die.
Montresor states that he must not only punish Fortunato, but punish with impunity. To do this he also says " A wrong is unredressed when retribution overtakes its redresser. It is equally unredressed when the avenger fails to make himself felt as such to him who has done the wrong." In other words, Montresor must exact his revenge without being caught by anyone but also in such a way that the person against whom the revenge is sought, understands full well that vengeance is being taken against him.
Fortunato's pride and arrogance make him an easy target for Montresor's plan. He is easily flattered and manipulated by Montresor's pretense of friendship, allowing Montresor to lead him deep into the catacombs without suspicion. Additionally, Fortunato's excessive consumption of alcohol weakens his senses and judgment, making it easier for Montresor to execute his revenge.
Montresor treats Fortunato with false concern and kindness, urging him to turn back due to the dampness of the catacombs. However, his true intentions are to lead Fortunato deeper into the tunnels to carry out his revenge.
The main characters in "The Cask of Amontillado" are Montresor, the narrator seeking revenge, and Fortunato, the victim lured into Montresor's trap. The story revolves around Montresor's elaborate plan to exact his revenge on Fortunato for an unspecified insult.
Montresor seeks revenge against Fortunato because he believes Fortunato has insulted and wronged him. Montresor's desire for revenge is fueled by his pride, perceived slights, and sense of entitlement.
The two parts are: one, he has to get away with it and two, he has to make sure the person who did the wrong in the first place knows he is paying for that wrong. This is how Montresor puts it in the first paragraph of the story: "I must not only punish, but punish with impunity. A wrong is unredressed when retribution overtakes its redresser. It is equally unredressed when the avenger fails to make himself felt as such to him who has done the wrong."
Pride is a characteristic shared by both men. Montresor's pride is wounded by Fortunato's insults, leading him to seek revenge. Fortunato's pride and arrogance make him dismiss the danger he's in, ultimately leading to his downfall.
Montresor does not describe "the perfect crime." Crime could mean anything from murder to robbery to assault. Montresor describes what is necessary to achieve complete revenge. According to Montresor, he wanted to exact revenge with impunity; however to do this two things were necessary. The person gaining revenge must do so without being caught and the person against whom revenge is being exacted must know that he is paying for his offense.
The main conflict in "The Cask of Amontillado" is between Montresor, who seeks revenge on Fortunato for an insult, and Fortunato, who is unsuspecting and unaware of Montresor's true intentions as he leads him deeper into the catacombs under false pretenses. This conflict drives the tension and suspense of the story as Montresor's dark plan unfolds.