In the short story by John Updike, entitled, "A&P," the falling action occurs after Sammy (the protagonist of the story) stands up for the girls who enter the grocery store where he works and are chastised by the manager for their attire (bathing suits). Sammy is turning a corner in his young life: this is a "rite of passage" story. Sammy sees the girls, especially the one he names "Queenie," and perhaps falls just a little in love—for she is like a queen, and he is mesmerized.
When they leave, Sammy finds that he cannot stand the fact that they have been scolded and sent on their way. Even though the rules state (as pointed out by the manager) that proper attire must be worn, Sammy cannot accept what has happened. He quits his job, though his manager tries to dissuade him—knowing Sammy's family.
"Sammy, you don't want to do this to your Mom and Dad," he tells me. It's true, I don't. But it seems to me that once you begin a gesture it's fatal not to go through with it.
Sammy, however, leaves the store and knows that from that moment on, nothing will be the same. This is the falling action of the story. It's like the lead up to Eve eating the apple in the Garden of Eden. It is a momentous decision (albeit a bad one) that is the pivotal point of that story. When all is said and done, a new, harder life is begun. This is the way it is with Sammy. He is grateful that he can make a "clean getaway." He goes outside and the girls are, of course, gone. He looks at the manager who has taken his spot in the checkout line, and Sammy knows there is no turning back: even looking at the manager, he may glimpse the complications that come with growing up.
...my stomach kind of fell as I felt how hard the world was going to be to me hereafter.
We are left to imagine that the youngster Sammy was when he came to work, now sees the world from a new perspective. The world will never be as simple and uncomplicated as it was when he arrived at the store to start his shift.