When is it over?
When is the story over?
Really over, I mean, as in "this is the last paragraph, and what comes next is 'The End' at the bottom of the page." This is usually some way after the big climax in which the central story problem is solved (they kill the dragon/blow up the Death Star/arrest the murderer), but how long after?
The answer, as usual, is: it varies. To some extent, it depends on the length of the story - a five page short story may be too long if there's more than half a page after the climax, but nearly every reader I know would feel that having only a page or two of wrap-up to a trilogy just wasn't enough. Similarly, if three pages out of the five are wrap-up, there's probably something wrong with the short story, while it may take five or ten chapters or more to do a proper job of wrapping up a complex trilogy.
The two obvious problems are stopping too soon, and carrying on too long. On the whole, I tend to think that too little is better than too much. A reader who finishes a book wishing there'd been just a little bit more is a reader who is likely to come back for the next one; a reader who gives up with a bored sigh two pages before "The End" appears under the last line of text is a reader who is likely to avoid the next one like the plague. And it really hurts to discover that you have overshot the end of the story by two or six or ten chapters, and that you must therefore cut all that material. For most of us, it's a lot easier and less painful to add a scene or a chapter than it is to cut one.
Nevertheless, most novels need a certain amount of post-climax wrap-up to be satisfying. A novel is a long haul, and many readers need to be eased out of it gently, so to speak. If it's a complex novel or a multi-book series (trilogy, quadrology, innumerable-fat-books-a-la-Jordan/Martin-series), there are likely to be a bunch of subplots and loose ends that need wrapping up, because they couldn't all be tied up neatly as part of the big climax. And since most novels follow the classic plot structure (a series of attempts by the protagonist to solve bigger and bigger problems, where each try ends with the protagonist in a worse situation than ever, until the very last one finally succeeds/fails for good), they need something at the end to reassure the reader that this time the protagonist finally pulled it off, and there isn't some nasty surprise waiting to turn the "ending" into a cliffhanger.
And finally, this part of the story - the part between the climax/solution and "The End" on the last page - is about consequences. This is the part that leads a lot of writers astray, I think, because in a lot of books the consequence of the protagonist's actions is that he/she moves on into a new life (or returns to an improved version of the old one). This looks and feels like a beginning - and it is. But it's the beginning of a new and different and unrelated story. The writer is allowed to tell that story, of course, but in the next book. The bit that goes at the end of this book is the acknowledgement that things have changed.
For instance, one writer I know was working on an action-adventure of the sort in which the protagonist is a junior space officer, faces a crisis, succeeds while annoying the top brass, and is "rewarded" with the captaincy of the worst ship in the fleet, posted to the worst spot in the galaxy, as a way of getting rid of him. Naturally, he goes on to shape up his new command, defeat new enemies (and make more political ones), and so on.
The problem was that this novel was approaching half a million words and the writer couldn't figure out how to cut it. But it didn't need cutting; it needed splitting into the several books that it actually was. The writer had run right through the ending of his first book (which occurred a quite reasonable 100,000 words or so into the story) and on into the next. All he had to do was stop at the point where the hero was notified that he was being promoted and given a new ship, but before showing the rust-bucket full of misfits that was his new command.
Part of the difficulty here was that the writer was so caught up in the "show, don't tell" advice that he thought he had to show the new command, which led directly into the next story, leaving him no good break point. But the other part was that after spending 100,000 words and many hours working on making the characters "feel real" and planning all the hero's future adventures, the writer had made them too real in his own head. Real people's lives rarely divide themselves up into neat episodes, and their stories don't end until they're dead.
The second reason too many wrap-ups drag on is that the writer is trying to give attention to every single subplot and character individually, one scene or chapter per subplot. This is as unwise as it is unnecessary, especially in a book with lots of characters and subplots. A lot of long goodbyes and subplot finishes don't make these things seem more important; they make the scenes feel thin. It's often more effective to pack two subplot resolutions and a couple what-these-characters-do-next into the same scene, and then do some summarizing, than to have four or five long scenes to show each character moving into his/her new life and another three or four to resolve subplots. Alternatively, a series of mini-scenes - a two-to-three-paragraph look in per character to hint at where they're heading now - can be very effective for a complicated, cast-of-thousands book or series, as long as they're mini-scenes.
Finally, a lot of writers keep going in search of the boffo ending line, sometimes whole chapters past wherever the story should have cut off. Don't do this. Just don't. It never ends well.
