Why is Montresor an unreliable narrator?
Montresor controls the story we receive. He claims to have endured injuries and an insult, yet supplies no independent account of them and gives Fortunato no opportunity to explain. His elaborate revenge is therefore not evidence that his grievance was justified. It is evidence of the explanation he chooses to give his listener.
The gap between his stated principles and his actions is especially revealing. He presents revenge as something that must be completed without punishment and understood by its victim. Yet the narrative leaves questions about what Fortunato understands, what the listener knows, and why Montresor tells the story after so much time. These uncertainties make his confident manner worth examining.
Calling him unreliable does not require proving that every event is fabricated. A narrator can accurately describe actions while distorting motives, omitting context, or inviting an unjustified moral conclusion. The useful reading question is not simply whether to believe him, but which claims the text supports and which depend entirely on his self-serving account. The first printing lets readers inspect that distinction in Poe’s wording.
Sources and further reading
Editorial answer from Ask Poe. Interpretive readings are distinguished from documented publication facts. Check the linked texts and editions.