He argues that a short story should be read in one sitting, allowing the reader to experience the carefully constructed atmosphere and emotions without disruption. Any break in the reading process disrupts the flow of the narrative and diminishes the impact of the author's intended effect.
Here's how he puts it:
> "It is only with the last sentence, the last line, that the reader is to determine whether the writer has succeeded in doing what he set out to do. If, before the closing sentence, the reader begins to guess, or divine the intention, he is at once put off his guard, and, losing all his interest, is in a state of mind far from that which the writer intended."
This emphasizes the importance of a carefully planned and executed narrative, where every element contributes to the overall effect. Interruption disrupts this carefully crafted experience, breaking the reader's immersion in the story.
Therefore, according to Poe, a story loses its unity of effect, emotional impact, and the reader's engagement when interrupted.