We know that Montresor is a proud man when he says that the reason he kills Fortunato is because "he ventured on insult". In other words, once Fortunato insulted Montresor, Fortunato could not forgive him and he decided to reek revenge on poor Fortunato. The persuasive techinique Montresor uses are also very ingenious. He appeals to Fortunato's ego when he keeps repeating, "Oh, there is always Luchesi". Fortunato considers himself an expert on fine wine and is not about to let Luchesi or anyone else verify whether Montresor's wine is Amontillado or not. Finally, the idea of revenge is present throughout the story. At the beginning, Montresor says that "redress must not overtake the redressor. I must punish[ Fortunato] and punish him with impunity." Montresor has planned his revenge very carefully so he will not get caught. As he takes Fortunato a further and further into his vaults, Fortunato makes the sign of a mason, a selective and secretive group of businessmen. When Montresor doesn't understand the sign because he's not a mason, Montresor says, "Yes. I'm a mason." and pulls out a trowel, a tool of a common mason. This shows he plans to wall up Fortunato all along and it was not simply a whim.