Montresor has an understanding of human nature. He manipulates Fortunato into going into the crypt by telling him that he has a special cask of wine. Just in case telling him about the wine will not be enough, he tells him that he will go to someone else to ask about to wine. He knows that will pique Fortunato’s interest.
“As you are engaged, I am on my way to Luchesi. If any one has a critical turn it is he. He will tell me—”
“Luchesi cannot tell Amontillado from Sherry.”
“And yet some fools will have it that his taste is a match for your own.”
Montresor knows that when he tells Forunato that he has his doubts about the authenticity of the wine, and he is going to Luchesi, he will get Fortunato to volunteer and he won’t be suspicious. It’s human nature! He has pricked Fortunato’s pride by not asking him, and also gotten him interested in the wine and made him feel like he will be left out if indeed the wine is genuine! It is a double-threat.
It is “the supreme madness of the carnival season,” so that everything is kind of crazy. People will not be paying attention as carefully. This is one of the reasons that Fortunato chooses this day. Fortunato has his guard down. Also, Montresor knows he can get his servants out of the house.
I had told them that I should not return until the morning, and had given them explicit orders not to stir from the house. These orders were sufficient, I well knew, to insure their immediate disappearance, one and all, as soon as my back was turned.
By doing this, Montresor ensures his alibi. No one knows whether he is home or not. He has told his servants to make sure that they are home, so they will all think that he is supposed to be home, and if anyone asks if he was home they will all say he was.
Finally, Montresor messes with Fortunato’s head within the crypt. He pretends he belongs to the Masons, an old fraternity, and asks about his health a lot. He makes a joke about the Masons to explain the trowel. He actually will need the trowel to brick up the wall where he will entomb Fortunato. His concerns about Fortunato’s health will again reduce his suspicion.
They say that sociopaths are the best profilers of human nature. They may be crazy and homicidal, but they can read other people like a book, push their buttons, and manipulate them. Montresor used his knowledge of people, his uncanny ability to read human nature, to plan the perfect murder and get away with it. What is revenge if you get caught? Montresor may be crazy, but he isn’t stupid. Whatever insult Fortunato did to him was obviously so small that he was unaware of it. He paid for it with his life. Clearly Fortunato was not as good a judge of people as Montresor.