By telling the events of the story out of chronological order, Ambrose Bierce sets the scene for the reader, establishes the stakes, and creates the opportunity for a surprise ending.

The story of "An Occurrence at Owl Creek Bridge" is something that takes place in moments at the eponymous bridge. If Bierce had started with the main character's ambitions and past, it would have been a completely different story. He started at the moment the story begins—the final moments of the condemned man on the bridge.

By starting at this moment, Bierce also establishes the stakes of the story. It's an opening that catches a reader's attention and lets them know immediately that someone is possibly going to die. It helps establish narrative tension and keeps the reader interested in the story.

Finally, Bierce's story is meant to be a little confusing and otherworldly. The main character believes that events are happening that aren't; he isn't diving into the river to escape and get home to his wife. Instead, he is going to die at the hands of the soldiers. Moving the reader through different times and events helps give them the same kind of confusion that Peyton is experiencing. They can be convinced that what Peyton believes is actually true and then are surprised when he is actually dying, hung from the bridge.

It's not just the hapless Peyton Farquhar whose mind has been playing tricks on him, but the readers', too. Thanks to Bierce's shuffling of time frames, we find it impossible to work out the difference between fantasy and illusion. That is, until right at the very end of the story when it's finally revealed that Farquhar didn't return home to his loving wife after all but is about to be hanged by Union troops.

One of the story's themes is the often fine line between fantasy and reality, and Bierce realizes that exploring this theme is facilitated by a disruption of chronology. Had the story been told in strict chronological order, then all we would've been left with with was a rather humdrum story about a foolish fellow who allowed himself to be tricked into committing an act of sabotage and paid the ultimate price for it.

As it is, however, we're presented with something much more interesting—a narrative that operates on so many different levels. As well as giving us an insight into the psychology of people in wartime, Bierce's fractured narrative allows him to explore the nature of fantasy and reality and how the relationship between them operates in cases where people are under extreme pressure.

In his story “An Occurrence at Owl Creek Bridge,” Ambrose Bierce disrupts normal chronological order, placing news of the successful hanging – which takes place very early in purely chronological terms – at the very end of the tale itself.  Bierce arranges the story this way for a number of reasons, including the following:

• By doing so, he creates suspense. During much of the story, readers are tricked into thinking that Peyton Farquhar has survived the attempt to hang him and that he is successfully making his way toward home.
• By structuring the story in this way, Bierce plays tricks with the reader’s perceptions and sense of reality in the same way that Farquhar himself is tricked by his own mind and fantasies.
• By imposing this kind of structure on the story, Bierce catches readers in a sudden, abrupt surprise, a surprise similar in some ways to the one Farquhar suffers when his body suddenly falls to its death.
• By ordering the story as he does, Bierce is able to give us a great amount of background information about Farquhar’s personality, aspirations, and mode of living, so that we come to “know” Farquhar and his life even as he is in the split-second process of dying.
• The present structure of the story allows Bierce to take tiny moment of Farquhar’s life and expand it enormously. Farquhar’s final second comes to seem, in many ways, the richest and most intense experience of his whole existence. This is especially the case as Farquhar fantasizes that he has managed to escape to his home and that he sees his wife:

As he pushes open the gate and passes up the wide white walk, he sees a flutter of female garments; his wife, looking fresh and cool and sweet, steps down from the veranda to meet him. At the bottom of the steps she stands waiting, with a smile of ineffable joy, an attitude of matchless grace and dignity. Ah, how beautiful she is! He springs forward with extended arms. As he is about to clasp her he feels a stunning blow upon the back of the neck; a blinding white light blazes all about him with a sound like the shock of a cannon--then all is darkness and silence!

Peyton Farquhar was dead; his body, with a broken neck, swung gently from side to side beneath the timbers of the Owl Creek bridge.

• By structuring the story as he does, Bierce punctures any romantic illusions the reader may have been entertaining.  Just as Farquhar’s romanticism is brutally undercut, so is the reader’s.

 In short, Bierce has many good reasons -- both artistic and psychological -- for structuring the story as he does.