The character in Poe's "The Cask of Amontillado" with the ironical name of Fortunato is the possessor of personality traits that are, indeed, his nemesis. In fact, he is easily duped because of these faults:
- He imbibes so much that he is incapable of logical reasoning and clear perception. When, for example, Montresor takes him farther and farther into the catacombs, the drunken Fortunato does not stop to wonder why they are proceeding so far.
- He is vain, believing himself a great connossieur of wine, one whose opinion should be valued over that of others.
- He is petty. Fortunato does not want anyone to taste the Amontillado because he wants to be the one to judge it and take credit for having done so. Determined to not let his rival Luchesi taste the wine before he does, Fortunato becomes myopic in his thoughts as he risks his health in the damp catacombs filled with miter just to prevent Luchesi from tasting the Amontillado.
- He is deluded in his judgment of Montresor, suspecting no ulterior motives from a competitor. As a result, he is easy prey for his enemy who lures him deeper and deeper into the catacombs of his family. When Montresor protests, Fortunato foolishly takes Montresor literally, saying that he is fine and there is no need to call Luchesi--"[he]is an ignormamus"--and is totally stunned when Montresor walls him in.
I think it was simply his drunken state and his gullibility that makes him such an easy target