Short stories are bouncy little things, in comparison to novels. I’ve blogged before here about the sense one has as a novel progresses (assuming one has not already set things down in stone in an inviolable outline) that options constrict after the climax of a novel, during the falling action. They never quite disappear of course, but there’s a sense of momentum that shoves the story along and gives a sense of inevitability. One can play around with that sense, and even frustrate it, but it’s there. Even when you get to the end and it’s not what you expected halfway in, it feels as if it’s been on its way for a while.
Short stories, not so much. The one I’m working on now is a couple of hundred words from the end, and I’m trying on endings like Imelda Marcos tried on shoes.
I think what happened is that I confused, in my mind, the main plot twist with the ending. I got as far as the twist in my head when I plotted it out and said to myself, “and that’s the end.” It isn’t. O. Henry structures are not always viable these days. The twist is necessary but not sufficient, as it were, to the ending.