So, the question – what is the point and purpose of a flashback?
A flashback is usually a revelation of character, is it not? It shows us something in the past that helps to explain a character’s current state. We see the character, we see a flashback, and then we feel differently about that character. It would be as if we were sitting in a therapy session with Sybil and Dr. Wilbur and we cut to flashbacks of Sybil’s abused childhood. We’re forced to see her being tied up and beaten by her schizophrenic mother, see her being locked in a box, see her endure those horrific enemas and then be tied to a piano by her mother and be told to “hold it in.” Those flashbacks would be absolutely essential to her story, would they not? We would never forget them. It would be far more effective to SEE her childhood than to HEAR Sybil talk about it in therapy, right? By watching those scenes, we would feel even more sympathy for that poor girl.
I’ve read books that argued against the famous flashback in Casablanca. Bogart drinks at night after having seen Bergman enter his gin joint, and we go to the flashback of their love affair. We see how much they were in love, how much he loved her, and of course, the “wow finish,” and Bogart's stunned disbelief at the train station. Then we’re back to the present. Bergman shows up. I love that flashback. I don’t remember the names of the books that argued against it, as I threw them out years ago. In any case, they argued that it was pointless and slowed the narrative. They’re all wrong. The flashback showed us a love affair that we wanted to see, and it made us feel some of Bogart’s pain. It earned him sympathy. Otherwise, we might’ve been put off by Bogart’s lashing out at Bergman.
By its very design, a flashback reveals. They are usually short, emotionally charged, and show us things that illuminate that character’s current state. They impress upon us something we would not have felt while we watched this character in the present.
I love flashbacks. But the question we’re asking ourselves is, “can a flashback be stretched to 120 minutes?” Can it be structure? By making it structure, you’re forced as a writer to show a character very briefly in the beginning, like Fred MacMurray in Double Indemnity, who’s in a pickle, and then you're forced to jump right into two hours of revelation emphasizing all the hows and whys just to explain the reason MacMurray wound up in that pickle.
Wouldn’t you say that Shakespeare emphasized better the hows and whys of Romeo & Juliet’s tragedy without having a flashback structure?
Every play of Shakespeare contains elements of tragedy, some foretold, some not (“Antony & Cleopatra” comes to mind). We, of course, remember most his famous chorus that sang of “star-crost lovers” taking their lives at the beginning of “Romeo & Juliet.”
But he never EVER opened a play with his final scene.