The key to understanding Poe's "The Tell-Tale Heart" is in what one critic terms "the principle of redundancy and repetition." For, in this repetition--notably even the title repeats "Tell" with the homonym "Tale"--the underlying motif of the story emerges. Truly, the narrator is obsessed with the old man's eye as a symbol of haunting death and implacable time, and this obsession ties to the narrator's "I" as he joins the old man in a death-watch. For, "the hellish tattoo of the heart" that increases the old man's terror also intensifies the "uncontrollable terror" of the narrator, who himself is tortured by the thought of death.
The old man's terror must have been extreme! It grew louder, I say, louder every moment! ... I have told you that I am nervous; so I am....amid the dreadful silence...so strange a noise as this excited me to uncontrollable terror.
Thus, in order to escape "the curse of time and mortality" symbolized by the "hellish tattoo" of the heart and the morbidity of death pall of the "hideous veil" of the"vulture eye," the narrator kills the "eye" as he would like to halt the torture of his own "I." But, unfortunately for the narrator, the death of the old man does not terminate his own torture.
And, so, what the murderer perceives as the ticking of the old man's heart is, in fact, the ticking of his own heart in his identification with the old man as a mortal cursed. Since his killing of the old man has not alleviated his own death-terror. without the old man, the narrator now applies the principle of "redundancy and repetition" to the policemen, placing them in his former position and himself in that of the old man who feels terror in his death-watch. So overcome with psychological terror is the narrator that again he feels compelled to arrest the "hellish tattoo," but this time it is his own heart. In his death-and-time-obsessed agony, he is driven to confess his deed,
They were making a mockery of my horror! Anything was more tolerable that this derision! I could bear those hypocritical smiles no longer!
He tells the tale of his murder and orders the police to tear up the planks, displacing his own horror onto the "beating of [the old man's] hideous heart, hoping that the revelation of his crime will end his psychological terror of implacable time and death.