Considered the master of the short story, Edgar Allan Poe insisted that unity of effect is absolutely essential to the success of a story. Indeed, all the elements of a story, plot, point of view, theme, setting (the prime elements) tone, flashbacks, foreshadowing, irony, symbolism, imagery, etc. must be directed towards this single effect, Poe contends. Nor can the value of brevity be diminished, either; yet a story cannot be so short that it lacks enough momentum to produce a powerful impact.
The basic elements of stories are the keys by which the author designs a story; usually one of these is the prime element used. For instance, in Poe's short story, "The Cask of Amontillado," the point of view of an unreliable first person narrator directs the unity of effect. The other elements of plot, setting, and theme support this point of view as the narrator in his horrific design against the man he perceives as his enemy directs him into the macabre setting and bizarre psychological toying of his victim as, for example, Montesor, the narrator, puns on the word mason and displays his family's sinister coat of arms. In fact, all of the narrator's actions and words and their momentum are directed to the single act of fettering his victim Fortunato and walling him in for eternity. And, yet, the momentum of these actions and words of Montresor--produced so cleverly with the aid of tone, foreshadowing, irony, imagery, and symbolism--create ironically the most powerful effect of this Gothic story: the real horror of "The Cask of Amontillado" lies, not in the conventions of Gothicism, but in what human beings themselves are capable.
In regard to Poe's poetry, this has been written,
According to Poe, therefore, the principles of composition are precise, logical, and impersonal, even though the end in view is the evocation of intense psychic excitement.
But, these principles can certainly be applied to the composition of the short story. For, it too must be precise as every line should, as William Faulkner advised, build character or advance the action toward a singleness of effect.
(The links below provide additional information on the composition of the short story.)