Do you think the insult really happend or did it just exist in Montresor's head?

This is a subjective question. Many readers will see the
answer to this question differently based upon personal interpretation. Therefore, the
answer to the question will be subjective as
well.

Montresor, from Poe's "The Cask of Amontillado", has
spent the past fifty years contemplating the insult enacted upon him by Fortunato. One
could look at this in two very different ways.

First, one
could justify that Montresor is insane. His insanity stems from the fact that he has
been obsessed with the insult placed upon his name by Fortunato. From this obsession
stems insanity.

Second, one could look at Montersor's
desire to seek revenge on Fortunato as a simply act. Fortunato wronged Montersor and,
therefore, deserved death.

Lastly, one could examine
Montresor's reaction to impending concealment in the tombs. Fortunato begins to scream.
Montresor suddenly worries that someone may hear the screams. Montresor stops bricking
up the wall. He becomes fearful of being caught. One could look at this in two different
ways. First, Montersor is conscious of what he is doing is wrong; therefore, he is sane.
Or, secondly, Montersor is insane given he begins to scream along with
Fortunato.