The pattern of story set up followed by dramatic pay off is one of the chief engines of forward motion in a story, pulling the reader along for the ride. One of the components of this forward motion is the element of surprise, when a dramatic element placed earlier in the story returns to complicate or complete a later action. Think for a moment about Chekhov’s gun. Imagine that we see it on the wall in the first act, and then the moment the audience sees it, a character pulls it down from the wall and shoots someone. End of story. Chekhov’s gun can be used to demonstrate many dramatic principles, one of them being the importance of letting an element placed early in a story generate suspense under the surface, the reader subconsciously wondering if it’s going to mean anything, then to return to that element later, paying it off. Dramatic spacing generates more suspense, and greater eventual power, when the story turns sharply on the dramatic event that fulfills the set up.
When you pay off a story element, include another set up in the pay off, or cut immediately to another set up. This propels the reader through the text because each set up creates a mystery that the reader wants to see solved. The reader gets pleasure from anticipating the answers to these questions. If you solve the mystery the moment it's posed, it gives little pleasure to the reader.