What makes an ending “The End”?
In a word: closure.
At the end of the story, whether the heroine won or lost, she’s not going to get another chance to try. The Evil Overlord is gone for good, the wedding is on (or off), the murderer has been discovered and arrested. There may be some loose ends, but the main thing is over and done with…whatever “the main thing” is for that particular story.
In order to achieve this, the story first has to provide a question that needs answering, or a problem that needs settling. Will the hero get the girl? Will the detective catch the murderer? Will the Evil Overlord get a date for the prom? The ending is the moment that provides the answer, whether that answer is Yes, No, or even Maybe.
That may seem obvious, but a lot of the beginner stories I see fail to present a central problem or a main question, and as a result they have serious difficulty finding a point of closure. Mostly, they end up sort of petering out and stopping, and their authors agonize over their inability to write endings. But their problem isn’t really with their ending - the problem is that they never set up anything that could come to an end point. You can’t close a door if no one ever opened it in the first place. The only fix for this is to rewrite the piece around a problem or question, so that there’s something to answer and a way to end. So that it’s a story and not just an incident.
Other writers overshoot the end because they’re looking for the perfect boffo closing line. It’s lovely when one gets a boffo line to end on, but it doesn’t always happen…and it’s usually much more effective to stop at a reasonable point than it is to make readers slog on through pages or chapters of filler, waiting for a punch line. The flip side of this is writers who cut things off abruptly as soon as the main problem is solved, without providing any wrap-up validation (of which more anon).
Still other writers string their endings out - first the scene with the action climax, where the heroine kills the dragon; then a scene for the big revelation, where the hero tells her he’s not her long-lost brother; then the emotional climax, where one of them proposes; then a scene for the climax of the secondary plot-thread, where the grand vizier runs off with the kitchen maid; and so on. Sometimes one does have to handle each thing separately, but it is often more effective if one can figure out how to bring as many of the threads together in one scene as possible, and tie them all up at once. Unlikely as it may be for the hero to propose in the middle of fighting the dragon while the vizier and kitchen maid try to sneak past the fray without getting killed, it’s often more convincing as a climax or ending scene (if, of course, one can pull it off). At the very least, the revelation and the proposal can usually go in the same scene.
The last mistake I see a good deal of is writers who don’t provide any wrap-up or validation after the big climax scene. Wrap-up is the bit where you let the reader find out how some of the minor subplots turned out, or what happened to other interesting characters while the hero and heroine were busy with the dragon, or where you tie up any loose ends that are still flapping around now that the main plot-problem is solved. Validation is something to let the reader know that it really is all over now; they really did succeed. In my standard plot outline, the ending is usually described as “there is a big fight and the good guys win; this is followed by awards and weddings, as appropriate.” The “big fight and the good guys win” is the action climax; the “awards and weddings” is the validation. If you get a medal, it means you really did win…for this book, anyway.