The narrator is so determined that he has deluded himself into believing that his mental disease is actually making him more conscious and aware. In fact, his so-called focus is extreme paranoia and anxiety. The narrator claims to love the old man but in his neurosis, he justifies his intention to kill the old man because he cannot stand to be looked at by the man's eye. He justifies this intent to kill based on how determined and focused he is in going about the murder. His mad determination overrides this love he has for the old man.
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!
He is determined to kill only when the old man's eye is open. He returns seven times, sneaking into the man's room, only to retreat because the eye is closed. On the eighth night, he is in the room and the old man wakes up. He remains perfectly still. He takes pride in how slowly and stealthily he opens the lantern to catch a glimpse of the old man's eye.
The narrator continually tries to convince the reader that he is not mad; rather, he is determined and dedicated to a purpose. "If still you think me mad, you will think so no longer when I describe the wise precautions I took for the concealment of the body." His determination and calculation to carry out and get away with the murder consume him. The twist at the end of the story is that the paranoia shifts (perhaps to guilt or fear) and he abandons his determination to avoid being caught; it would seem that in the end, he is actually determined to be caught by the police.
Thank you! This will really help me with my homework!