If you can’t find an ending to your WIP, there is only ever one reason for it:  something hasn’t worked earlier on.
 
I’ve reached the end of novels, novellas and short stories in a variety of different ways:

1. I knew the ending first and have been leading up to it confidently from the beginning
2. I had a vague idea of what should happen but had to work on it once I got there
3. I knew what was supposed to happen but couldn’t figure out how to get there
4. I had no idea where the story was going
5. I had no idea how to end once I ran out of story

 
Every story is different.  No one way of writing is better than another.  For all my novels, I plan my endings to avoid waffling on endlessly.  I want to lead the reader confidently towards an ending that will either surprise them, please them, or leave them thoughtful (better still – wanting to read more if it’s a series).  This is something that works for me.  I like to know where I’m going.  I want to know what’s going to happen to my characters.  This way I can work on nuances and hints and ironies while I write.  Sometimes the ending can go flat when I get there, having held it in my head for so long, but a bit of rewriting, rethinking and reworking soon rekindles the original fire.
 
My short story writing is more experimental so I’m ready to expect the unexpected.  There can also be something quite delightful about not knowing the ending to a story.  It’s like embarking on an adventure and discovering things as you go along.  Not knowing your ending doesn’t mean you’re going to get stuck.  In a wild creative urge (and your muse on top form), a brilliant ending can occur to you just when you need it. 
 
While I’m definitely NOT going to advocate that you MUST know your ending before you start, there are going to be times when you just can’t find an ending – even if you planned one!  It’s awful if a planned ending doesn’t work but it’s worse if you just can’t think of a way to end a piece.  I don’t suffer from writer’s block but I come close to it when I hit a total blank at what I realise must be the end of the story.  How do you even know if you’ve reached the end of the story?  Has the plot run out?  Are all the characters dead?!  Or are you just sick of it? 
 
Whatever the problem, my Big Writing Tip should work.  Before I get to it, let me take you through some writing experiences I’ve had:
 
Knowing the ending
All my novels were carefully constructed.  I didn’t necessarily know them scene-by-scene and interesting things often occurred along the way, with some characters proving more alive than others, but I knew where I was going.  My Fleet Quintet novels were immensely complex with a plot that spanned hundreds of years (actually millions!) and some wild leaps in time.  I carried the plot of five novels around in my head for years and it was a great relief when I finally finished the fourth one.  The fifth novel in the Quintet is yet to be written but I have all the notes:  I know exactly what it is going to happen because I know exactly where all the plot holes are that need to be filled, the dangling threads that need to be tied up, the mysteries yet to be solved.  This is all planned!
 
Finding the ending years later
This has happened to me several times.  My short story, The Evolving, which I wrote in my early twenties, was rewritten decades later with an altered ending that actually made sense.  Another short story, Walked (which had a different title), was written in the late nineties but the ending was deeply unsatisfactory.  I knew the MC had to get to the desert in a plane, but what did she find there?  Over ten years later, the story became part of The Exodus Sequence and the ending resolved perfectly.  It was as if the story had to wait for the right ending to coming along!  Another Exodus Sequence story, Crashed, had a very weak ending that I couldn’t resolve.  By applying my Big Writing Tip, I finally found the perfect ending years later.  But I had to really work for it!
 
Not knowing the ending
My short story, Diamonds on the Moon, is a relatively unstructured piece which I didn’t plan at all.  I started with a dragon waking up on the moon, trapped in a crater, wondering what his purpose in life was.  I had NO idea where this was going.  I certainly hadn’t planned for Neil Armstrong to turn up in it!  I really just wanted to write about beauty and joy and friendship and I think I succeeded with that.  The final sentences of the story capture a theme that is prevalent throughout my writing (which means the ending worked for me, though I can’t be sure it works for anyone else!)  I planned nothing, yet the story is definitely finished and finished on a high note too, despite the sadness.
 
No ending at all
A recently completed Exodus Sequence story (which will appear in a collection of short stories as well as the second Exodus volume) (eventually) began very strongly indeed.  With characters that leapt off the page and felt very alive, it was great fun to write.  But once they reached their goal, knocking on the front door of a forest cabin they were trying to find and conversing with the inhabitant within – what then?  I had no idea!  Where was the story going?  What were they trying to do?  Why was this person in a cabin important?  I couldn’t answer any of these questions and was clueless as to how I was going to end the story.  I continued on boldly until finally I ran out of steam.  I’d rather hoped something would occur to me before I reached the ending, but it didn’t.  So I abandoned it for a while, then applied my Tip, and ended up with something more brilliant than I could ever have hoped for.  It moved the whole Exodus Sequence forward, rather than reaching the dead end of plot stagnation which is where I’d left it.
 
Having an ending come to me out of the blue
This is utterly brilliant when it happens.  It’s what you dream of as a writer.  It’s creation at it’s most excellent.  It also hardly ever happens.  I wrote Experienced pretty much “off the cuff” as it were.  There was no planning.  I launched into it wildly, then had to stop and restart the whole thing because I needed to change it into first-person-weird.  If you read it, you’ll know what I mean by “weird” because it’s a very dense story and takes a while for the confusing claustrophobic drug comedown to wear off and the plot to emerge.  The reader is basically walking in the MCs exactly footsteps – there’s no space from him.  You’re so far inside his head that you couldn’t escape if you wanted to.  For me, the revelation came during the fight at the end.  I knew what the MC had to do during the fight.  I just didn’t expect him to end up on real-world Io (that weeny volcanic moon that spins around Jupiter), nor did I expect that very last scene.  It absolutely tears me apart!
 
BIG WRITING TIP
 
If you can’t find an ending to your WIP, there is only ever one reason for it:  something hasn’t worked earlier on.
 
Oh, wait, didn’t I already say this at the beginning of this article?  Well, yes.  Because my Big Writing Tip isn’t more complicated than that.  It’s not some big secret thing.  It has nothing to do with inspiration, creative ability or your muse.  I’m quite sure there are a zillion other articles out there with advice.  Perhaps I’m saying exactly the same thing.  Perhaps I’ve come up with something genius.  But honestly, this is just what I’ve done and it’s worked for me.  Hopefully it’ll work for you.
 
If you’re stuck and in despair, the first thing you need to do is walk away from it for a bit.  It doesn’t matter how long.  If you can’t stand the story anymore, then make it quite a long bit.  You may just need a cup of tea or you may need to abandon it for years.  But if you don’t want to do the latter, try this:

1. Read the story from the beginning and make notes.  It doesn’t matter where or how:  I like using plain text documents.  But I’ve also been known to handwrite notes in vast volumes.
2. Ask painful questions while you read:  Does the plot make sense?  Do you know your characters well?  Do they remain “in-character” as it were?  Do you know what they want?  Do you even LIKE the story and where it’s going?  Is there an earlier scene that suggests a way out for the character and an ending to the story?
3. If you’ve had ideas while writing of earlier events that need changing, then change them now.  Sometimes if you spot a plot flaw, you’re not going to be able to think clearly until that flaw is cleared up. 
4. During this particular edit (it may be the first time the story is edited), you will almost certainly find things that don’t work.  Plot flaws, character errors, missing elements, maybe even a lack of structure.  You may find your tense is wrong or it should be in a different voice (first person rather than third).  You may even find the style is all wrong for the story and that it needs to be hard ass noir rather than wishy-washy fantasy (that would be quite an extreme change, but you get the idea!)
5. By now you’ve done a huge edit on your story, you’ve rewritten it, you’ve changed it, you found a new character or deleted one, your MC has expanded a bit and you know them inside out, you know their goals and dreams and past mistakes, you KNOW your story.  Has an ending miraculously suggested itself to you yet?  If it hasn’t, then there is still something missing from the story – and it’s not the ending that’s missing, it’s something earlier!  Find it and add it and connect it to the end.  There’s your story.

 
I’m currently working on a new short story for the Exodus Sequence about an MC from a previous short story, Woken.  His name also crops up in various other stories, so I thought I knew him quite well.  In this new story, he’s found dead on a beach in ancient Greece by a hermit – except that he isn’t dead and he has a huge story to tell.  The purpose of this story is to tell the truth about Atlantis (at least, the truth according to my Exodus Sequence universe!).  I launched in with no plot, no particular idea of which characters were going to do what.  I had some scenes in my head that I wanted to have play out.  And I knew that at the end, the hermit leaves his tiny Greek island and goes off to find some big name, like, I don’t know, how about Plato, to tell his story to, which is how Plato found the idea for his Atlantis.  That ending is all well and good, but what about the ending of the story that the MC relates?  That is the ending that is eluding me completely.
 
I already know there are some huge problems with the structure of the story.  It doesn’t have one!  It lurches about with info dumps and static conversations between characters.  I hate it!  Worse still, I don’t have all my facts straight.  The Exodus Sequence is a huge story with many characters, spanning millions of years.  Most of the stories are concentrated in the present or future.  Shattered takes place at the time of the Neanderthals and Woken in Arthurian times.  But this one, while set in the hermit’s time of ancient Greece at the time of Plato, also has a huge chunk set long, long, long ago, when there weren’t supposed to be any people on this planet at all.  It’s the heart of my Atlantis story, the soul of the Exodus Sequence.  The “thing” that happens here affects everyone forever more.
 
No pressure in getting it right, then!
 
What I’ve been doing is rereading ALL the stories in the Exodus Sequence and making historical notes.  I started this a few years ago and forgot about it.  Basically, I’m working on canon.  If the story has been published, which most of them are, then I can’t change the history.  And there is a lot of it!  It’s going to be very useful indeed to have all the “history” in one place with casual references to past events recorded in a linear fashion (to make my life easier.)
 
This is excessive when it comes to doing homework in order to find an ending to a story that has stalled, but it shows you how far I’ll go to get it right.  Hopefully, your story is just a one-off and just requires some serious editing.  By working on the Exodus universe history, or canon, I’ve already got a thousand ideas of how to fix up the story.  Better still, I’ve found the ending!  I realised my MC can’t possibly know who traps him.  THAT was the plot flaw.  It also means that in a future story, I can have a big revelation when he finds out who it is.  No writing is ever wasted!

​In which I kill a jogger. Well. Nearly.

You’d think that in the middle of a world pandemic, you’d want to avoid apocalyptic television!  But this was so good that despite its grim subject, I kept going to the end.
There were two things that struck me about that made it so very good:  the first occurred in the second episode, after the attack on Earth.  A main character started a journey across London on foot.  The camera tracked back and you saw all the bodies lying scattered everywhere, cars (no longer working) parked at odd angles, the world come to a dead stop.
It was a devastating scene.  Watching it just days after the lockdown came into force made it so much more terrifying.  It foreshadowed exactly those first few days of the lockdown when the streets were suddenly empty of traffic and you tried frantically to avoid anyone out for a walk in case they breathed on you.
What made it so brilliant was the unearthly silence.  And this is the second thing that struck me about this series:  the quiet.  The silence.  The muted scenes.  Unlike your usual end-of-world movie, there was no screaming, no crashing sounds of destruction, no weapons fire, no overwhelming Hans Zimmer-style soundtrack.  This alien invasion was a horrible, silent, creeping thing and this is what made this version of a very well-known tale stand way above any other production.
And there have been a few!  Wasn’t it just the other day I was watching a BBC production set when it was actually supposed to be set:  in the Edwardian era.  It seemed quite promising at first.  The female lead was set up as a strong character and the production looked good.  But it seemed to go awry somehow and I got very tired of that dusty red future we kept cutting to, particularly as there seemed to be no story.  And suddenly our heroine was almost superfluous.  The plot kind of ran out of steam and whatever it was trying to say was rather lost.
The Fox TV series has fewer pretensions.  Set in the current day in France (with subtitles!) and England (I kept trying to work out where in London they were but it was actually filmed in Bristol!), it was a world instantly recognisable, one in which the viewer could quite easily identify with and ask:  what would I do if this invasion happened to me.  There are no heroes.  The main characters are not always likeable.  The story seems to both crawl and race at the same time, and sometimes there seems to be very little story.  Tension levels are either high or very high, with no breathing space ever.  Events played out in crap hotel rooms or empty streets, or a French observatory.  The aliens look kind of stupid, to be honest, and they are actually stupid, resembling metallic dog-things that creak ominously when they walk.  And yet they proved to be really scary, particularly as they never seem to miss when they shoot.
 
It doesn’t sound all that promising when I tell you the characters spend quite a lot of time walking, but this is Walking While Very Tense.  The unravelling of character’s individual storylines was made more interesting by the lack of soap-style drama, into which this never descended.  Most captivating of all was the overriding mystery:  a blind girl hears a weird noise, can see again, has some kind of connection with the aliens and you know that tattoo she gets right at the beginning of the series?  HAH!
 
I found myself screeching and tearing my hair out when the end credits came up at the end of the last episode.  Was this the END??  But, no, there is a second series coming.  I can’t wait.