answer:
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.