Another fine mess...

combustion--the point in a short story or novel where dramatic elements collide with sufficient force to provoke action leading to a conclusion; the aggregation of forces prior to denouement; the literal and figurative boiling over of story.

A useful metaphor: story is a crucible into which such elements as characters and their agendas, opposing forces, surprise, reversal, and shifts of power have been added and the heat of plot inertia is applied. The pressure becomes so great that the story combusts, explodes, boils over, leaving the characters to clean up the mess, which is to say effect some kind of resolution, however permanent or temporary.

Most stories, longform or short, have combustion points; those that do not can profit from them. An excellent example of the combustion point in a short story occurs in Tobias Wolff's "Bullet in the Brain," where Anders has already been introduced as the point of view through whom the story is told, the bank robber is introduced, and the animosity between Anders and the bank robber set in motion. One combustion point comes when the bank robber fires a gun. A combustion point in a longer work occurs in the film, The Third Man, written by Graham Greene. The combustion point is viewable on You Tube (Third Man/Ferris wheel scene). Holly Martens, the protagonist, meets his old friend Harry Lime in a gondola car of a large Ferris wheel in the Vienna amusement park and Lime delivers his now iconic disquisition on the Swiss and the cuckoo clock. As a result of this cynical observation from Lime, a line is drawn in the moral sand between the two friends.

Each combustion introduces the element of change into the respective stories cited here, nudging each to its unique conclusion. The chemistry becomes: combustion causes change which forces outcome.

Hint: Aggravate, drive, tease, torment the characters to a point where one or more of them moves beyond what he or she appears able to take, causing the behavior that will make some things irrevocable, sweeping safer options off the table. Characters who are always in control ultimately tire the reader. Characters who appear to have breaking points concern the reader. Characters who either discover or are driven to an interior place they did not know they had become permanent residents in the readers' mind.