Edgar Allan Poe’s narrator in his short story The Tell-Tale Heart lives with a kindly old man, whom the narrator emphasizes, he actually holds in high regard: “I loved the old man. He had never wronged me. He had never given me insult.” This fondness, however, is insufficient to keep the old man in the narrator’s good graces because of the old man’s eye. Poe’s narrator is obsessed with one of the old man’s eyes, which he describes early in the story as resembling “that of a vulture—a pale blue eye, with a film over,” and emphasizing, for good measure, “Whenever it fell upon me, my blood ran cold . . .” Driven essentially insane, his protestations notwithstanding, by the eye, the narrator decides he must kill the old man. For much of the story, the narrator describes in intricate detail the measures he plans to take to effect his roommate’s demise. This, then, is what the narrator does every night, and why. Every night, while the old man sleeps, the narrator peeks into his room, establishing a pattern that will facilitate the execution of this particular mission. As he describes his nightly activity,
“. . .every night, about midnight, I turned the latch of his door and opened it—oh, so gently! And then, when I had made an opening sufficient for my head, I put in a dark lantern, all closed, closed, so that no light shone out, and then I thrust in my head.”
After a week of such activity, “upon the eighth night,” the narrator finally sneaks into the old man’s room, accidentally waking him in the process, and proceeds to attack and kill the source of his angst. The answer to the question, in short, is that the narrator, every night for a week, peeked into the old man’s room to ensure himself of his intended target’s sleep pattern.
The narrator of the story is driven mad by the "vulture eye". So each night he opens the lantern ever so slightly so that light will shine upon the eye and he can observe the man as he sleeps. He wanted to make sure he was asleep at the same time each night before the murder, to ensure it went well.
To allay any suspicions that his intended victim might have, the narrator greeted the old man each morning during the week before the crime with encouraging words, asking him about how he had slept the night before. But each midnight as the old man slept, the narrator carefully lifted the latch on his bedroom door, moved his head inside the room itself, and opened a lantern’s shutter so slightly that only a narrow beam of light pinpointed the ‘‘vulture’’ eye.