The May, 1842 edition of Graham’s Magazine contains a review of Volume 2 of Nathaniel Hawthorne's collection of short stories entitled Twice-Told Tales. The review was written by Edgar Allan Poe, in which Poe first proposes his theory of writing short stories that has since become known as Poe's "single effect" theory.
A skillful literary artist has constructed a tale. If wise he has not fashioned his thoughts to accommodate his incidents; but having conceived, with deliberate care, a certain unique or single effect to be wrought out, he then invents such incidents—he then combines such events as may best aid him in establishing this preconceived effect.
Poe elaborates on his "single effect" theory in a subsequent essay entitled "The Philosophy of Composition," which was published in Graham's Magazine in April, 1846, in which Poe analyzes his poem "The Raven" with regard to his "single effect" theory.
Poe's "single effect" theory presents certain rules or guidelines that Poe believes are necessary to follow in order to write an effective short story. For example, Poe proposes that the story must be written to be read in one sitting of one-half hour to two hours, and no longer, which he believes reinforces the "totality" of the "single effect" of the story. Poe believes that every sentence in the story must build toward and contribute directly to the "single effect" of the story and that the first sentence is of utmost importance to the rest of the story.
If his very initial sentence tend not to the outbringing of this effect, then he has failed in his first step.
Poe emphasizes originality, brevity, and the totality of the story as essential elements of an effective short story. Poe equates writing a short story with painting a portrait, in which every word, like every brushstroke, contributes to the final, single effect of the story and the portrait as a whole.
This is the first sentence of Poe's short story "The Tell-Tale-Heart":
TRUE!—NERVOUS—VERY, very dreadfully nervous I had been and am; but why will you say that I am mad?
This sentence tells the reader that the narrator is "dreadfully nervous" for reasons as yet unknown, and someone, or perhaps more than one person, has told him that he's "mad," also for reasons as yet unknown.
The question of the madness of the narrator becomes, and remains, the focus of the story. The purpose of the story, the "single effect" of the story, is the exploration of the depth of the narrator's madness.
The madness of the narrator remains the underlying issue throughout the story, and true to his own theory, Poe introduces other issues during the course of the story that support and reinforce that single effect.
The first of these is the issue of the murder of the old man. Poe creates considerable suspense in the reader's mind while the narrator formulates, explains, and finally executes his plan to murder the old man. The second issue involves the suspense that's engendered by the seemingly interminable wait for the murder to be discovered, or, in the telling of the story of "The Tell-Tale Heart," revealed by the murderer himself.
In revealing the murder, the narrator reveals the true depth of his madness, and Poe achieves the single effect that he introduces in the first sentence of the story.