The narrator spends a great deal of time trying to convince his reader that he is not, in fact, mad. The evidence that he relies on is mainly his calm, calculated approach to the crime. He plans the event very carefully and patiently, to such an extreme that it seems to confirm his claim to sanity. He describes spending an entire hour each night opening the old man’s door, for example—not to mention the irrationality of killing the man because of his eye. Ultimately, the narrator’s madness, and his inability to identify that madness, causes him to admit to his crime.