"hearty tone" every morning and asking him how he passed the night. This would suggest that speaker is capable of lying—he obviously does not mention that he has been spying on the old man. He manages to deceive the police, as well, until his guilt overcomes him.

We know very little about the old man except that he lives in the same house with the speaker and has his own bedroom. He is terrified one night when he hears the narrator in his bedroom. Otherwise, we have no knowledge about him or any reason to believe he should be feared. The narrator doesn't seem to perceive the old man as fully human.

The speaker is motivated to kill the old man, he says, because he has the eye of a vulture. The speaker states it is not the old man he wants to kill, but his evil eye. He looks in on the old man every night, wanting to murder him, but he can't, because the old man's eyes are closed. One night, however, after having disturbed and frightened the old man, he shines the light of the lantern in his room, as he does every night. This time, it falls on the old man's open eye, and the speaker can hear the old man's heart beating loudly, so he kills him.

The narrator's own guilty feelings trip him up. Although he has declared the old man "stone dead" and has buried him beneath the floorboards, the speaker believes, after the police come, that he hears the beating of the old man's heart. It seems to get louder and louder, until he believes the police are mocking him by pretending not to hear it. Therefore, he confesses his crime:

"Villains!" I shrieked, "dissemble no more! I admit the deed! —tear up the planks! here, here!"

In “The Tell-Tale Heart” by Edgar Allan Poe, the narrator’s primary purpose entails convincing the reader that he is not insane.  The nameless speaker provides few details to enable to reader to visualize him physically; however, he speaks to his internal purpose and finds excuses for his behavior at every turn.

The narrator  is unreliable. Unreliable narrators are compelling because they represent a basic aspect of being human. All people have moments of confusion or memory loss. Sometimes it is difficult to be absolutely accurate about the events of even the most important situation.  This story takes this unreliability to new heights.  Because the speaker wants to justify his actions so that he is not judged as mentally unstable, the truth of the story is questionable from his point of view. Yet, his perverse view is all that the reader has.

The singular effect of this irrational narrator impacts the course of the story. Hyperbole finds the narrator convinced that his intense hearing ability enables him to hear “all things in the heaven and in the earth and many things in hell.”

This is a sick mind that  has the responsibility for the care of an elderly man.  Eventually, the narrator murders the old man. The reader learns everything about the murder through the narrator’s version of reality. Further, the narrator would like the reader to think that he is omniscient in his ability to see into the mind of the old man.  Here is an example:

‘Presently I heard a slight groan, and I knew it was the groan of mortal terror…I knew the sound well. Many a night… it has welled up from my own bosom.’

The narrator's insight into the man's head just reflects his own experience. This narrator is paranoid, mentally ill, highly nervous, and unable to distinguish what is real or unreal.  Apparently, friendless and alone, the man never sleeps. His nights are spent weirdly watching the old man laying his bed.

I could scarcely contain my feelings of triumph. To think that there I was, opening the door, little by little, and he not even to dream of my secret deeds or thoughts.

The reader must surf through the narrator’s minutiae to understand that his reasons for murder.  Despite his best efforts, this insane speaker’s action cannot be justified. Without any other information provided, the reader looks at the events with the singular view of the insane narrator.

Poe could have told this story from a few different perspectives. The events of the story would have passed just about the same had Poe chosen to use a third person omniscient narrator. The difference would have been in how the reader judged the main character. That guy would have come across as a weirdo and nut case. He is a bit anyway, but Poe chose to use first person narration. By having the weird guy be the narrator, the reader immediately assumes the teller of the story is a good guy and reliable. It's not until the middle of the story that the reader starts to question the validity of the information being given by the narrator. But by that time the reader has already established a report with the narrator and is hesitant to change his or her initial judgment.

Another reason that I find the narrator convincing is that he has relatable personality quirks. Haven't you ever been bothered by some little odd character trait of someone that you know? In high school I was friends with a person, but I couldn't stand her laugh. It was like nails on a chalkboard. That's like the narrator and his master's eye. Of course I didn't kill my friend, so that makes me different. 

He is also convincing because of how quickly guilt takes hold. Again, I can relate. Even if my action was an accident, if it hurt someone and I can't fix it, I feel SO guilty. And often I only feel better after confessing or apologizing. And that's what happens to the narrator. His guilt makes him hear the heart beat until he confesses. Poe effectively walks the narrator through thoughts and emotions that I can empathize with, so that makes the narrator convincing to me.