Fortunato has laughed at my proud name! He shall pay for this! I'll get revenge on him... soon...
Fortunato loves good wine, I'll use wine to get my revenge!
The readers know Montrestor's motives, and Fortunato does not.
"And also the wrong would not be made right unless Fortunato knew that he was paying and knew who was forcing him to pay."
"Fortunato was a strong man, a man to be feared. But he had one great weakness: he liked to drink good wine, and indeed he drank much of it. So he knew a lot about fine wines, and proudly believed that he was a trained judge of them. I, too, knew old wines well, and I bought the best I could find. And wine, I thought, wine would give me my revenge!"
The reader must get to know the villain as well as they know the heroine.
"It was almost dark, one evening in the spring, when I met Fortunato in the street alone."
The weather reflects emotions and attitudes of the characters
"I heard only a soft, low sound, a half-cry of fear. My heart grew sick; it must have been the cold. I hurried to force the last stone into its position. And I put the old bones again in a pile against the wall. For half a century now no human hand has touched them. May he rest in peace!
The dramatic end is the result of Montrestor getting revenge on Fortunato.