Neff has the whole thing sewed up, with little pink ribbons, like Keyes would say. But, then, instead of just killing Phyllis and leaving, he goes through the whole spiel telling Phyllis his plan, leaving himself open to getting shot first.
Stupid. Neff should have just shot her. Zachetti would have shown up to a dead Phyllis with the cops right behind him. Case closed. Neff would be a free man.
But, instead, he just has to rub it in with her, and let her shoot him first.
A great deal of the most beloved fiction, whether on the page, the stage or the screen, hinges on bad decisions, stupid mistakes and surrendering to compulsion. Without them, some of our best films would be only about ten minutes long. Walter's narration begins with citations of two compulsions. "I killed him for money, and for a woman." Greed and sex: two of the most primal human instincts, immediately recognizable and understood by every adult viewer.
Other things we learn about him in the course of the story is that he's weak and corruptible, in spite of thinking of himself as something of a hotshot who's more clever than he actually is. It takes him almost the entire story to realize he's been manipulated, outmaneuvered and betrayed by Phyllis every step of the way, from the very start.
When he resolves to devise a plan to help her kill her husband, he believes it's been his idea, and as he lays it out for her, he describes "Nothing sloppy, nothing weak." In the end, he discovers he's been both. So, yeah, he can't resist yet another compulsion: revealing to her how he's cleverly figured it all out, and taunting her with his final clever plan.
And yet, he still hasn't fully understood the kind of person he's dealing with, and is brought down by his own hubris. Which, incidentally, is a classic theme in drama and lore going back to Greek mythology.
It's this ultimate realization that restores his basic decency and humanity. Even wounded, he could just as easily have stuck to his plan and let Nino walk into that house to be framed for Phyllis's murder, but he already understands what Keyes will so tersely articulate for him in just a few hours: he's "all washed up." He's then free to surrender to two more compulsions: altruism (or self-sacrifice, if you like) and confession. He could still have attempted his plan to head straight for the border if he wanted, but he must unburden himself to Keyes.
That's one way of looking at it, but it's dramatically sound if the screenplay finds motivations within the characters to justify it. I think this one does.
And how uninteresting so many films would be without those things they sometimes need to happen.
This is all richly layered thematic material, and only scratches the surface of the depth and complexity that Billy Wilder and Raymond Chandler brought to James M. Cain's story in adapting it for the screen.
Yet, they did so by eliminating subplots and some quite florid melodrama from Cain's novella, streamlining the dramatic curve and boiling all motivations down to basic human drives and instincts needing no explanation. And all of it within the constraints of the all-powerful Production Code Administration which, under the dictatorial control of Joseph Breen, had deemed the book unfilmable since its 1935 publication. Even Wilder's frequent writing partner, Charles Brackett, passed on collaborating on it, considering the story altogether too sordid. Indeed, the novella's wild and rather perverse conclusion is quite far removed from that of the film, but is chilling and haunting in its own way. It's a brisk read at only 110 pages or so, and I recommend it.
While some of Cain's prose tended to be overblown, there's one line in the book I wish could have found its way into the screenplay, into which it would have fit perfectly: “That's all it takes, one drop of fear to curdle love into hate.”