Why is the narrator of The Tell-Tale Heart unreliable?
The narrator asks us to accept a conclusion that the account repeatedly undermines. Careful planning and heightened hearing are offered as evidence of sanity, while the stated motive centers on the old man’s eye. The narrator’s confidence does not make the explanation reasonable or independently verifiable.
The final sound is especially important. We hear about the heartbeat only through the narrator. The police officers’ conversation is interpreted as mockery, but the story does not independently establish that they hear the sound or know where the body is hidden. The confession follows the narrator’s interpretation of the scene.
Unreliability here is a relationship between a voice and its evidence. It need not mean that every described action is false, and it does not require the reader to assign a modern diagnosis. Ask what the narrator observes, what is inferred, and what is merely asserted. That method reveals how an attempt at self-defense becomes self-exposure. Poe lets the voice perform its own contradiction instead of supplying an outside narrator who explains it away.
Sources and further reading
Editorial answer from Ask Poe. Interpretive readings are distinguished from documented publication facts. Check the linked texts and editions.