Several times Montresor ask Fortunato to turn back. Why would he do this when he is deliberately plotting his murder?
It has often been said that Montresor uses "negative psychology" on Fortunato when he urges him to turn back. The idea is that some people will insist on doing just the opposite of what another advises, just out of obstinacy and contrariness. Orneriness. Fortunato is very drunk. It is commonly observed that drunks can be very obstinate and hard to handle. To take an example from our times, a friend may be obviously too intoxicated to drive home, but the more you try to get him to stay put and sleep it off, or to let someone else drive him home, the more he insists on driving himself.
But Fortunato has another reason for wanting to press on. If he leaves before tasting the nonexistent Amontillado, then Montresor will go to Luchesi.
“My friend, no; I will not impose upon your good nature. I perceive you have an engagement. Luchesi—”
We will go back; you will be ill, and I cannot be responsible. Besides, there is Luchesi—”
Montresor has demonstrated that he wants to get a connoisseur to judge his nonexistent wine that very night. It is either Fortunato or Luchesi. Why is Montresor in such a hurry? It must be because he thinks he got a bargain and wants to buy more of this nonexistent Amontillado before word gets around that it is available at a bargain price. Why? He wants to sell it as a profit. He may not even like Amontillado sherry. It is a sweet liquor. A ladies' drink. His "pipe" contains 126 gallons which he could turn into 500 quart bottles. Ostensibly he would like to buy one or two more casks and make two or three times as much profit. He needs money.
Fortunato is only interested in the bargain too. He is not a wine sipper but a wine guzzler. He is a rich man and could buy the entire cargo and make a small fortune. He doesn't want Luchesi to hear about this bargain-priced shipment because Luchesi would be thinking the same thing. And Luchesi is probably also a rich man.
Further, as noted by Winston-Smith, by suggesting that they turn back, Montresor creates the impression that he has no ulterior motive in going forward. By showing such concern for his victim's health, he masks his intention to kill him.
Fortunato may be a good judge of wine, but he probably has no intention of telling Montresor the truth--that is, if the wine turns out to be genuine Amontillado. He will take a sip, lick his lips, shake his head and assure his friend that it is only ordinary sherry, thus eliminating Montresor as a competitive bidder and preventing Montresor from mentioning the nonexistent Amontillado to anybody else--especially to Luchesi.
Edgar Allen Poe’s “The Cask of Amatillado” has become a classic tale of revenge as told by the unreliable narrator of Montresor. Montresor feels that he has been wronged by Fortunato and uses Fortunato’s ego to lure him to his death. Montresor in his revenge seems to take an action that is counter to his murderous intent; he insists that he and Fortunato return because of Fortunato’s health.
Montresor suggests that Fortunato turn back for two reasons; one being that if Fortunato continues on it is his own fault and Montresor’s conscience can take some solace in that, second he gives Fortunato the option to go back to lure him in further without raising any suspicion.
"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 Luchresi --"
By Montresor giving Fortunato a way out Montresor can blame Fortunato for his own death. This blaming Fortunato may seem strange, however, it is Fortunato’s ego that keeps him going even after having a severe coughing fit. Montresor uses Fortunato’s pride in his wine expertise to lure him to his death. Luchresi is mentioned as being knowledgeable about wine, yet Fortunato cannot be upstaged by Luchresi even to the detriment of his health. Fortunato’s pressing forward can allow Montresor to place blame on Fortunato.
Because Montresor gives Fortunato the option to turn back, Fortunato has no reason to suspect his “Friend”. Montresor seems to be very concerned with Fortunato’s health that there is no reason to doubt his intentions.