True! — nervous — very, very dreadfully nervous I had been and am; but why will you say that I am mad? The disease had sharpened my senses — not destroyed — not dulled them.

This very first line of the story introduces the narrator’s lack of insight to his own irrational thought processes.  Here he suggests that he cannot possibly be mad because of his sharpened senses, and yet, by the end of the tale, it seems what the narrator mistakes for external input actually comes from within himself. We see this most clearly with the heartbeat he hears at the very end, which he mistakes for the old man’s. Most likely, he hears his own heartbeat racing in his anxiety, or at the very least hallucinates the sound from his guilt.

You fancy me mad. Madmen know nothing. But you should have seen me. You should have seen how wisely I proceeded — with what caution — with what foresight — with what dissimulation I went to work!

The narrator makes this statement before describing his process of sneaking into the old man’s room at night. Once again, his definition of madness does not match up with the way the story explores madness. The narrator focuses entirely on his demeanor, as if the way he does an action determines whether it was rational. However, because his underlying belief in the evil of the old man’s eye and his murderous solution are not rational actions or behaviors, the way he enacts them are irrelevant to the sanity of his actions.