They both seem to start with some type of loss and end with a type of madness.
There are so many elements incorporated into his stories that it would be impossible to understand them all after one reading.
The reason is unknown. Fortunato, someone of a similar wealthy stature as that of Montresor, acted in a way that could not be tolerated after he insulted Montresor. He writes his stories in a way that engages the mind and questions character.
What makes this story so popular can be seen in the way it was written. He plans to entomb Fortunato in the catacombs below his house, and he establishes a set of guidelines for a successful revenge.
Montresor tried to commit a crime in order to extract revenge.
Poe also uses first person, where the narrator is the protagonist who is deeply involved. We would also understand what causes this type of behavior. It fulfills human curiosity; at least the curiosity to know what it would be like to be buried alive.
He tells his plan step by step of how he commits this dexterous murder.