No, he wasn't insane, just very revengeful.
It is suggested in Edgar Allan Poe's story "The Cask of Amontillado" that Fortunato insulted or wronged Montresor in some way, although the specific details of the offense are not explicitly stated. This offense likely involved a significant betrayal or humiliation that fueled Montresor's desire for revenge.
No. Quite the contrary in fact - which promotes the reader to suspect that the narrator is insane.
The best evidence to support the claim that Montresor is insane is his meticulous planning and execution of Fortunato's murder without showing any remorse or guilt. Additionally, his enjoyment of inflicting pain and suffering on Fortunato further indicates his mental instability. Finally, his delusional belief that the murder was justified and necessary demonstrates a clear disconnect from reality.
In the opening line, Montresor states that he has suffered a thousand injuries at the hand of Fortunato but now Fortunato has also insulted him and this is too much to take, so Montresor plots revenge. There is an indication that Montresor is insane because there is doubt that Fortunato has ever injured or insulted Montresor at all. Montresor does not describe a single incident of injury nor does he describe the insult that supposedly has pushed him over the edge. Why would Montresor suffer a thousand injuries but plot revenge after only an insult? Aren't injuries more serious than insults? Wouldn't sticks and stones break Montresor's bones but words can never hurt him? Why plan to murder someone after an insult but not after all those injuries? Later when they meet at the carnival, Fortunato is very friendly toward Montresor. He hardly acts toward Montresor like he has injured him a thousand times and has just recently insulted him. Wouldn't Fortunato have said something to Montresor about the insult or about all those injuries he has laid on him in the past? Darn right, he would have, but he doesn't. Fortunato acts like they are the best of friends. Not only does Fortunato act friendly, but then volunteers to leave the carnival to go with Montresor to his home to test the Amontillado. Sure, Fortunato's vanity in being a connoisseur is part of that willingness, but surely, he would not have been so cheerful in doing Montresor such a favor. Finally, Fortunato, this supposed enemy of Montreesor goes down into Montresor's cellar without the slightest bit of trepidation about being all alone in the dark cellar with someone he has supposedly injured and insulted. Fortunato's action completely belie the idea that he is an enemy of Montresor. The one conclusion the reader can draw from the contradiction between Montresor's words and Fortunato's actions is that the injuries and insults Montresor mentioned are all in his head and that he is quite insane.
Poe omits details in order to suggest that there are no details, which would mean that Montresor is somewhat insane for plotting a murder of someone who has done nothing to him.
Montresor is an unreliable narrator because there are indications that he is either insane or the possessor of an overactive imagination. The indications come from Montresor's words and Fortunato's actions. Montresor begins the story by telling that he has suffered a thousand injuries at the hand of Fortunato , but now Fortunato has also insulted him. For that, Montresor seeks revenge and plans to murder Fortunato. The problem is that Montresor gives no details of these injuries or insults, leaving the reader to wonder if he is imagining all of it. Another indication that no such behavior ever occurred is found in Fortunato's behavior when he runs into Montresor at the carnival. Fortunato is friendly and gracious. He offers to leave the carnival to help Montresor test this Amontillado Montresor says he might have. In the cellar Fortunato suspects nothing untoward from Montresor even though they discuss Montresor's family motto which is that they will not allow anyone to insult the family. Surely, if Fortunato had acted so badly toward Montresor he would not have offered his help and would not have been so blind to the possibility that Montresor would uphold the family honor deep down in the cellar where Montresor could exact revenge with no one knowing about it. And that is just what happens.
David Montresor's birth name is David Edward Montresor Read.
Frederick Montresor was born in 1811.
Montresor believes that fortunato has repeatedly insulted him
Maxminio Montresor was born on 1980-03-03.
Frederick Montresor died on 1887-12-15.
Robert Montresor Rogers was born in 1834.