In "The Cask of Amontillado," Montressor also knows how to push Fortunato's buttons. Montressor determines that he will use Fortunato's greatest weakness--his love of wine--to his own advantage. He knows that Fortunato will not be able resist the tempation of tasting a rare and unseasonal bottle of Amontillado, so he dangles it as the proverbial carrot before the rabbit. Montressor also uses the carnival to his advantage. Montressor knows that Fortunato will be drinking and that in his inebriated state he will be more likely to fall for his plan. With most of the town at the carnival (including Montressor's servants), witnesses will be unlikely.
To me, there is one thing about Fortunato that we can see clearly and one that we have to guess at. Both of these seem to have some role in making him fall prey to Montresor.
The clearly evident one is his pride. Montresor keeps giving him the chance to just go home but his pride won't let him. Montresor keeps saying that he'll go get Luchesi to see whether the wine is really amontillado. But Fortunato is too proud to let this happen.
The thing that we have to guess at is why Fortunato doesn't know Montresor hates him. One guess is that Fortunato is too arrogant and stuck on himself to even think about how others see him. Maybe he never even thinks about how his actions affect others like Montresor.
its not clear as to what fortunato had done to to fall prey to montressor but montressor did say in the beginning of the story "The thousand injuries of Fortuato I had borne as I best could, but when he ventured upon insult I vowed revenge."
the time and place picked by montressor and the reverse psychology used on fortunato didn't make him suspect his fate. his pride could be taken into consideration
luchresi is fortunato's enemy and when montressor mentions that luchresi is more capable of telling the difference between the wines and fortunato doesn't know the difference between sherry and amontillado that drives him to montressors mansion