In the second paragraph of Edgar Allan Poe's short story "The Tell-Tale Heart," the wholly unreliable narrator—who, despite his protestations to the contrary, is clearly insane— explains his reason for killing the old man who lives in the house with him.
"It is impossible to say how first the idea entered my brain," the narrator writes, "but once conceived, it haunted me day and night. Object there was none. " The narrator begins by writing that he had no reason, no "object," for killing the old man, even while he explains why he killed him.
"Passion there was none," he writes, although, as the story unfolds, it's apparent that he's passionate about killing the old man who he also admits he loves but whose declaration of love is negated by the fact that he kills him.
The narrator notes, "He had never given me insult," although it's evident from his act of killing the old man that the narrator took offense at something that prompted the narrator to kill him.
I think it was his eye! yes, it was this! He had the eye of a vulture—a pale blue eye, with a film over it. Whenever it fell upon me, my blood ran cold; and so by degrees—very gradually—I made up my mind to take the life of the old man, and thus rid myself of the eye forever.
There it is. The reason that the narrator kills the old man is to rid himself of what he later calls the old man's "Evil eye."
Or is it the reason he kills him?
As the story unfolds, the narrator seems to forget about the old man's "Evil eye," his "vulture eye," and becomes increasingly obsessed with the old man's beating heart. At first, the old man's heart makes just a "low, dull, quick sound, such as a watch makes when enveloped in cotton," but the sound of the old man's beating heart grows increasingly louder, to a "hellish tattoo," and the narrator becomes increasingly terrified and increasingly furious at the sound.
But the berating grew louder, louder! I thought the heart must burst. And now a new anxiety seized me—the sound would be heard by a neighbour!
It's virtually impossible that a neighbor would hear the old man's beating heart, but with that irrational thought in his mind, and with the uncontrollable rage he feels toward the old man's beating heart, the narrator leaps out of hiding and into the old man's room. He drags the old man to the floor, and pulls his heavy bed over him, crushing and suffocating him. It's only then, after the old man's heart stops beating and he's dead, "stone dead," that the narrator again mentions the old man's "Evil eye."
His eye would trouble me no more.
Ridding himself of the old man's "vulture eye" might have provided the initial motivation for the narrator to kill him, but it seems more like an afterthought now that the old man is dead. It's the old man's beating heart which ultimately enrages the narrator to such an extent that he commits murder, and it's the beating of the old man's heart that the narrator hears even after the old man's death that ultimately leads him to shout out his confession of the murder.
After all, Poe titled the story "The Tell-Tale Heart," not "The Evil Eye."