Montresor claims Fortunato's greatest strength is his knowledge as a wine connoisseur, stating that Fortunato--unlike most Italians--has a "true virtuoso spirit" and is "sincere" in his mastery of old wines. He also has a personality that inspires respect and fear in others. While flattering the drunken man in his wine cellar and feigning concern over his health, Montresor comments that Forunato is "rich, respected, admired, beloved" and a happy man who will be "missed." Whether or not this is true remains to be seen, but it certainly suggests something about Montresor's motives; not only is he vengeful, but also (it seems) quite jealous.
Fortunato's greatest weakness, however, is also a component of his strength: his love for wine. This indulgence becomes his ultimate downfall, as his inebriated state and interest in the alleged pipe of Amontillado leads him to foolishly follow Montresor to his wine cellar, where Montresor kills him by paving him behind a wall. Although perhaps less significant, Montresor also cites another flaw in Fortunato: he is a "quack" when it comes to painting and gemmary.
Throughout the story Montresor offers several descriptions of Fortunato that offer some insight into his reasons for wanting him dead. At the beginning of the story Montresor describes Fortunato as "a man to be respected and feared" although he has one major weak point. Montresor also describes Fortunato's knowledge and connoisseurship of paintings, gems, and wine. Although Fortunato's knowledge of wine is his strength, his love of wine (along with his susceptibility to flattery) is also his weakness. Montresor meets Fortunato late at night when he is already very drunk and convinces him to come down to his family's vaults to try a cask of rare Amontillado wine. Montresor convinces him through a mix of his love of wine, his pride, and his susceptibility to flattery to follow him, suggesting that without the help of Fortunato (or one of his rivals Luchesi) he will be unable to determine if the Amontillado is real. Once they go down into the vaults Montresor keeps Fortunato distracted with a mixture of wine and continued flattery. He flatters Fortunato saying that,
You are rich, respected, admired, beloved; you are happy, as once I was. You are a man to be missed. For me it is no matter.
This description of Fortunato serves to keep him distracted from Montresor's true plan, but also suggests some of Montresor's reasons for wanting him dead. Fortunato is successful, popular, and happy in a way that Montresor is not and he cannot bare this.
Montesor of Poe's "The Cask of Amontillado" states that Fortunato has a "weak point" in priding himself on his connossieurship in wine. But, like most Italians, Montesor continues, he does not have "the true virtuoso spirt," the deep interest in and knowledge of the art of winery. Like his fellow countrymen, according to Montesor, Fortunato is an opportunist who practices "imposture upon the British and Austrian millionaires," pretending enthusiasm for the sake of sales. In painting and knowledge of precious stones, Fortunato is "a quack." However, Fortunato is "skillful in the Italian vintages" like Montesor himself.
This last statement suggests a rivalry between Montesor and Fortunato. "The thousand injuries of Fortunato" he has "borne" seem much exaggerated by the unreliable narrator, Montesor.