Distracted by something else. That's one of the many reasons why I'm not trying to write anything too long at the moment.
I don't start a big project I don't plan on finishing, but with short stories it's usually distraction by a different idea, or lack of interest. Sometimes it's both put together.
This tends to happen to me if I don't plan it out properly. I used to be really good at just pantsing things but lately I get the story all tied in knots and end up tossing it out and starting over. I get to a point where I think "this has absolutely nothing to do with where I actually wanted the story to go. Why am I writing this again?" I'm getting better at it though. I can tell where I've made a wrong turn and need to go back and fix it more than I used to be able to. And I'm learning to take breaks rather than just scrap things, even if I do cannibalize it later on, because its easier to see the good stuff in the bad if I've had a break from it. I don't think I've ever given one up completely though. Even though most of the actual work gets tossed or rewritten later, I still hold onto the actual idea so that I can go back to it and write it when the time is right.
I've stopped writing a few short stories because they just weren't going to work and I wasn't interested enough to save them. Short stories for me usually need to get started and finished within a small span of time. If they fall out of that window, they don't usually make it. Granted, this has only happened a few times in total. I did almost give up on a novel once. I started my first novel, got about 1/4 of the way through, and totally lost steam, so I started something new. Problem is, the reason I lost steam was that I had no real discipline and wasn't really that good at writing. I worked out a routine and decided to try to finish my first one. I succeeded, but the second one was left dangling, only a couple chapters in. With a writing routine figured out, I moved on to two new novels over the course of the following year and saw them through from beginning to end. So at that point I figured, lemme go back and finish that old one that never got anywhere. That one is now my fourth novel. Now I have two new ones in their embryonic stages. One I intend to work on until completion. The other will probably be the next one once the first is finished. For novels, it takes a lot of forethought before I even decide to start. So unless I'm totally sold on the project, I won't waste time. As far as other projects, I've left many unfinished video games (RPG Maker is a lot of work!) and unfinished songs/albums. Don't know what I'm going to do about those, if anything.
When I have too much planed out. I really need something to discover as I'm writing, otherwise I get bored.
I certainly have many, many unfinished projects lying around, but I don't think of them as abandoned so much as, ah, deferred. I always make sure to get enough down that I won't forget what I was aiming for, but otherwise I don't stress too much if they languish for a while. Although in my case I'm new enough at this that I (hopefully) will be a lot better writer by the time I get around to finishing them.
I'll either get distracted or realize that the direction the project is going is not the right one. The latter is what I've been dealing with at the moment, and while my general plot can be salvaged there's enough work that I just need to start over.
I usually heed the siren call of another story. Just this summer I had started House of Cadre and abandoned it for In the Pit. Another reason I've abandoned stuff - I get anxious about the project, and fueled by an utter lack of confidence write it off as crap and start something else. I can't even use the story as an excuse as in I don't know what to write next, because I usually have some idea. It's usually just me and my moods derailing me.
All my unfinished work was abandoned because: 1) I was pantsing and suddenly didn't know where the story was going, 2) I lost confidence in myself as a writer, or 3) I saw my oh-so-original concept in someone else's work.
Most times I'll give up a story because it'll feel dull compared to another idea I have, or I just start to plainly dislike it too much and it's a lot of work to change it by that point, so I may as well start something new.
I find that confidence will ebb and flow for any given story, so if I stop working on one I don't think of it as 'giving it up' permanently but rather that I'm just taking a break from it. Sometimes that break can last years lol. I think if it was a good idea with a strong vibe to begin with, the writer can likely always regain that vibe later by 're-immersing' in that story. Like this one action-thriller story which I began many years ago but left unfinished: if I begin telling someone about it at the coffee shop, that original spark starts coming back and I get motivated to work on it again. But I can see that if someone's original fire for a story goes away for good, that may mean it may well never be revisited.
I take your point, Tea@3. My current WIP started as a drawing exercise in art college 30 years ago. It's hardly recognizable now, but it's still the same story... sort of... kind of...
I start a story sometimes before I really had a chance to think about it or flush out the possibilities. At times it is just not worth the time to waste on a non working story when I could be putting more effort into a project I actually have a belief/passion for that extend beyond the initial "I have a good story Idea" moment. I still keep a log of story ideas though, the good and the bad because one never knows when inspiration will present it's self.
It means you write without having any idea what will happen next. No planning, no outlines. Think of it like you're blindfolded and your characters have you by the hands and are guiding you to...something.
I would usually stop when a story isn't going in the direction that I wanted it to. I don't often plan what happens, just in parts. Or when I realize that the story has too weak of a plot to sustain itself. Real life can be another factor, starts leaking into my work, and the next thing I know, the comedic feel gets dampened until it gets depressing, and I can no longer think of any way to keep it hilarious. There is black comedy, and then there is the sudden, irreversible shift in depression. I have to find a happy medium between jumping into a story blind and planning, because doing outlines would do my stories in, too, because I guess I'd feel strangled by the "restraint" of an outline, I guess.
I agree with @Wild Knight, in the sense of writing more off the cuff, than following an outline. Gives the story a little more unpredictability adding to the excitement. Put a few of my first stories on the back burner. Mainly due to lack of mature knowledge for the subject matter. Though I shelved an erotica story that is a little over 11 years old now, due to the fact that I do not see it as a viable read for most people. That and it comes back around to the lack of maturity, but it managed to squeeze me of 30+ pages of story before it wilted. Guess one could say I have become more critical of my writing style and content since becoming a man and leaving behind the childish fantasies of a hormonal teen. Looking back on the old, I have been fairly decent at depicting the elements with in the story. Although I think in the past year I have gotten a bit better than that. As well as able to portray a story that has more complex elements in its characters and plot. Who knows, maybe one day I will go back to the old stuff and revamp them to reflect my understanding of how to write them.
Elmore Leonard said a writer has to get one million words under their belt before they begin to get a knack for their own writing.
I usually have thought about an idea for a while before I put anything on paper/document. At that point, I'm convinced the story will work and have never truly abandoned a story in the middle. There are definitely ideas that I have started to outline and put aside for years but I still believe in the core of the story and will one day go back to it. Or maybe it will get absorbed into another story, that happens a lot too. I have this one novel idea I came up with over three years ago and have gone back to it several times to continue to flesh out the outline and make good progress but it's just a novel I don't think I'm ready/capable of writing right now. I have finished stories and never went back to them though, but perhaps I will go back to them one day and have definitely recycled scenes, characters, concepts, etc from them.
I feel this happens a lot. I started watching The Expanse on SciFi... many elements I have noticed similarities in the world I am writing. I read forward in the book series the show is based on. Totally dispelled my reprehensions. I am confident in my originality. Sometimes we need to snuff out doubt by just getting confident, even cocky if it gets you false motivation (which is better than no motivation).
Haven't been writing seriously for long so haven't given up on any stories yet. If I did it would probably be because the spark had gone, though I don't envisage that happening because the theme is important to me.