What are some of Fortunato's weaknesses? How do you know?

Fortunato, Montresor's enemy and eventual victim in Poe's "The Cask of Amontillado," is not a very clearcut character to the reader, but he does exhibit a few character flaws according to Montresor's descriptions.
First of all, Fortunato is already drunk when he encounters Montresor, so he may have a weakness for alcohol. Related to his fondness for alcohol is Fortunato's excessive pride in his own knowledge of wine. Additionally, Montresor reports that Fortunato has somehow insulted him, but Fortunato is unaware of his offense. Two possible interpretations of this situation exist: it is possible that Montresor is an unstable person and he is oversensitive and overreactive, or it is possible that Fortunato has done something so hurtful to Montresor that his mistake leads him to his own death. If the second case is true, then another flaw of Fortunato's is his lack of self-awareness.