In Edgar Allan Poe's "The Cask of Amontillado," Montresor lures Fortunato into the catacombs. He uses the pretense of having acquired a "pipe of Amontillado" whose value he questions, and he plans to ask their mutual acquaintance, Luchesi, for his advice. As Montresor anticipates, Fortunato insists on inspecting the Amontillado himself because "Luchesi cannot tell Amontillado from Sherry."
In addition to being prideful about his knowledge of wine and even helpful (there is nothing to suggest that Fortunato has any negative feelings towards Montresor), Fortunato is sick and plagued with a hacking cough. He's also intoxicated and becomes more so when Montresor gives him more alcohol to help mend his cough against the damp catacombs.
When Fortunato first steps into the niche, he is unsteady from intoxication and bewildered by the turn of events. Montresor's actions completely confuse him, and he trusted the man enough to follow him deep into the catacombs without suspicion. Montresor takes advantage of Fortunato's so-called stupid bewilderment to clasp him in fetters (irons) and to begin walling him within the niche. At this point, Fortunato's state of mind turns to fear and desperation, but to no avail.
Poe is a master at creating characters who represent the darker aspects of the human condition; in this case, Montresor is influenced by his desire for revenge as a result of Fortunato's "thousand injuries" against him and whatever insult pushed Montresor to plan murder. Poe amps the suspense of the situation by never explaining those injuries or insults -- so we are left to wonder if the punishment meted out by Montresor in any way fit the crime allegedly committed by Fortunato.