Above all else, the murderous narrator of Edgar Allan Poe's "The Tell-Tale Heart" seems to have a single-minded attitude toward his task. Totally self-absorbed in the plot to kill the old man, the narrator can think of nothing else. The fact that the narrator has obviously descended into madness, despite his attempts to convince the reader otherwise, is a characteristic of many killers, who no longer perceive the differences between right and wrong. The narrator's admission that he "loved the old man" is another example of his mental unbalance. Like many murderers--sane or insane--a guilty conscience eventually comes into play; and after the narrator has committed the deed, his guilt, displayed by his hearing the old man's beating heart, turns the tables on him. Another example of the homicidal mind is the "doppelganger" effect. A doppelganger is a character who serves as another character's double; in this case, the narrator's evil twin is the old man, who he kills
"because he cannot stand himself, perhaps fearing becoming old or disfigured like him."