You will note that Montresor the narrator continually refers to Fortunato as "my friend," "my good friend," and "my poor friend" throughout the story. He is not being ironic. He wants what he calls impunity. He has conditioned himself to think of Fortunato as his good friend, and he must always speak of him as such to everyone because he wants to be above suspicion when his good friend turns up missing. Even Fortunato thinks Montresor considers him his very good friend. This seems to be what makes Montresor an especially effective enemy. Fortunato trusts him. Nobody will suspect Montresor of having anything to do with Fortunato's disappearance. Montresor is sure to keep asking about him and showing deep concern about him longer than anybody else.
Two parallel examples from classic literature can be found in Othello and King Lear. Iago poses as Othello's best friend, and Othello is completely deceived by him. He calls him "honest, honest Iago." Iago hates him bitterly and seeks to destroy him. Edmund in King Lear shows nothing but brotherly love for Edgar while he is doing his best to turn their father Gloucester against his trusting half-brother. In both these cases the friendly enemies are successful although they both come to bad ends themselves. Shakespeare teaches us that we should be awfully careful about picking our friends. Poor King Duncan thought Macbeth and Lady Macbeth both loved him. King Lear thought Goneril and Regan loved him deeply.
While Montresor speaks of the "thousand injuries" that he has suffered from Fortunato and vows revenge, there is no explication of what these injuries are. So, added to the fact that Montresor seeks retribution for the supposed wrongs done to him is also the possibility that he is not mentally stable. This condition, added to his clever manipulation of Fortunato's hubris, leads to the power of Montresor as an adversary.
After he accosts Fortunato in the celebratory streets, Montresor catches the reveler off guard by acting as those their encounter is by chance. Casually, then, he mentions that he has received a large cask of Amontillado:
"I have my doubts...and I was silly enough to pay the full Amontillado price without consulting you in the matter. You were not to be found, and I was fearful of losing a bargain."
Here he has captured the attention of Fortunato; then, Montresor acts as though he does not wish to inconvenience Fortunato, saying that he is on his way to Luchesi, who "has a critical turn." This remark certainly ignites Fortunato's pride, "Luchesi cannot tell Amontillado from sherry." Further, Montresor fuels Fortunato's professional jealousy as well as he tells the other man, "And yet some fools will have it that his taste is a match for your own." After this maneuver, Montresor dons a black mask of silk and "suffers him" to hurry together to his palazzo. With feigned concern, Montresor stops Fortunato repeatedly, solicitous of Fortunato's health as the niter causes the other to cough. As they reach the inner chambers, Montresor uses reverse psychology, halting Fortunato along the way out of a seeming anxiety for his acquaintance's health; once they reach a dark recess, Montresor fetters the feckless connoisseur, who is stunned by this cruel act. Then, he laughs, thinking that perhaps this reversal by Montresor is a joke. But, when he realizes that it is not so, Fortunato calls out, "For the love of God." "Yes," replies Montresor coldly, "for the love of God."
There are many literary works and films that employ a luring of one's victim as a method for horror. One such film has an occurrence that is somewhat similar to the luring of Fortunato to the tomb of his death. In Silence of the Lambs, for example, there is a male predator who tricks young women into helping him as he struggles with a couch, trying to put it into a van. When the young woman steps into the van with the couch prohibiting her exit, he locks the door and kidnaps her. Then, she is thrown into a pit where she cannot escape and will just be sedentary; in the meantime, she is well-fed so that she will get heavy and her skin will stretch. When she gains enough weight, the predator will dispense with her and use her skin for his creative genius.