In Edgar Allan Poe's "The Cask of Amontillado," we find that Montresor is a master manipulator. He uses reverse psychology to appear to feel one way (while actually having ulterior motives) in order to drive Fortunato to do as Montresor intends, delivering Fortunato easily to his doom.
Montresor's plan is structured on the knowledge that Fortunato (who he believes has wronged him in some way—though the reader never learns the details) is a lover of wines: it is his passion, and in this case, it will be his undoing.
He had a weak point—this Fortunato—although in other regards he was a man to be respected and even feared. He prided himself on his connoisseur-ship in wine.
Montresor wants to lure Fortunato down into the catacombs beneath his palazzo. It is the season of carnival, and when Montresor finds him, Fortunato is a little worse for wear—in that he is already drunk. His wits, then, are a little duller than they might be under normal circumstances. Montresor pretends that he does not want to inconvenience Fortunato by dragging him away to sample a bottle of the coveted amontillado, a kind of liquor—specifically, a sherry or wine. There is no bottle of amontillado, but Fortunato does not know this. He might even have wanted to test the liquor later...until Montresor throws out the name of "Luchesi," a competitor who also is known for having a fine reputation in the connosseuirship of wines.
Montresor keeps Fortunato on the trail of the Amontillado by threatening to allow Luchesi to sample it first...
Montresor knows Fortunato well enough that he can count on the other man's desire not to be bested (or beat out) by Luchesi. And so, Fortunato agrees to accompany Montresor at that very moment.
Another example of Montresor's use of reverse psychology is seen when the two men begin their decent to the catacombs, and several times throughout the journey Fortunato coughs. Montresor pretends to be extremely concerned for Fortunato's health and even offers to return "above ground" to guard the other man's well-being.
“Come,” I said, with decision, “we will go back; your health is precious. You are rich, respected, admired, beloved; you are happy, as once I was. You are a man to be missed. For me it is no matter. We will go back; you will be ill, and I cannot be responsible. Besides, there is Luchesi—”
“Enough,” he said; “the cough's a mere nothing; it will not kill me. I shall not die of a cough.”
“True—true,” I replied; “and, indeed, I had no intention of alarming you unnecessarily—but you should use all proper caution. A draught of this Medoc will defend us from the damps.
Montresor offers feigned concern for the other man's health. Then he again mentions Luchesi. (Ironically, Fortunato notes, "I shall not die of a cough.") Montresor further makes sure that Fortunato is pliable and willing to continue by providing him with more alcohol, guaranteeing that he remains inebriated, passive and weak.
Montresor cleverly—pathologically—manipulates Fortunato with reverse psychology in order to exact his revenge.
Montresor is well aware of the fact that Fortunato does not need to go with him to the underground vaults or catacombs in order to sample the Amontillado (if it existed). Once Fortunato learns that Amontillado is available for sale at a bargain price, he could easily find the seller for himself. No doubt a shipload of casks of Amontillado has just arrived in port (at least according to Montresor’s story). That ship (if it existed) would be easy for a man with Fortunato’s experience to find, and he could sample the wine aboard the ship and probably buy directly from the captain.
Montresor knows that Fortunato would think this way, because he has had plenty of dealings with the man in the past and has frequently been injured by him in business transactions. When Fortunato says, “Impossible!” he is only expressing his surprise that a shipload of gourmet wine should have arrived without his having heard about it. He assumes that he has missed out on this information because he has been drinking and carousing.
Montresor only entices Fortunato to his palazzo by telling him he is on his way to consult Luchesi. Fortunato doesn’t want Luchesi to hear about the shipload of Amontillado, because Luchesi would go searching for it on the waterfront himself. Then Fortunato would be competing with Luchesi in bargaining for the wine. Presumably either one of them would buy the entire shipload.
Poor Montresor would have bought more than one cask if he had been sure of its quality, but he could not afford to buy the entire cargo of wine under any circumstances. At best he could buy another cask or two (if it existed!). So Fortunato decides to go with Montresor. The alternative, if Luchesi had not been mentioned, would have been to find the ship and sample the wine aboard it. But now what Fortunato is probably planning is to taste Montresor’s wine, shake his head, and tell him it is only ordinary sherry—then go looking for the ship, having eliminated both Montresor and Luchesi as potential competitors. And when Fortunato had beaten his competitors out of all the valuable Amontillado, he would laugh and call it “an excellent jest.”
Montresor has suffered a thousand injuries because Fortunato is rich and well connected, while he himself is poor and an outsider, a Frenchman. Yet he has to maintain cordial relations with Fortunato because he needs him for advice, for co-op business deals, and for obtaining finders fees when he knows of some valuable potential deal such as a big estate sale but can't afford to buy himself. He also uses Fortunato for social connections and insider information. Montresor is largely an outsider, like Poe himself.