Why does Montresor feel justified in carrying out his plan against Fortunato?
Montresor is carrying out a vendetta against Fortunato, whom he claims has inflicted upon him a "thousand injuries." What these injuries are, the readers do not learn; they only learn Montresor's standards for revenge, with one of them being that the victim must not realize that he is avenged.
The unreliable narrator, Montresor, declares that he has made an effort to bear "the thousand injuries" inflicted upon him by Fortunato, and the listener who "so well know[s] the nature of [his] soul" supposedly understands that what he plans is justified. Montresor, then, outlines how his plan for how revenge must be enacted. After Montresor lures the deluded Fortunato deep into the vault and fetters him to the wall, he builds other walls around him, fitting stones and plastering them. At first, Fortunato cries out, but Montresor makes no comment. "For half a century no mortal has disturbed them [the rocks]." Montresor's revenge is com-plete.