Sometimes, no matter how good your story or your writing is, no matter how compelling the narrative and no matter how interesting the specific event you're retelling at any time, you mess it up.
You write something, spend days - weeks, possibly - crafting immaculately-constructed sentences, ensuring that every character acts precisely according to their motivations and personality, putting words into their mouths that David Mamet or William Shakespeare would weep with envy to see and all described with words of such poetic strength that Wordsworth would swoon.
And then you read it a day, a week later and realise it's all codswallop, horse-crap and balderdash.
You've broken cardinal rules of story-telling: you've created an info-dump; you've overused metaphors; you've overused adjectives, adverbs; you've overused ANYTHING; your dialogue now looks stilted and forced; people are reacting to what you imagined you wrote and not what you actually wrote.
In short, you read it and wonder how the hell you ever thought you could be capable of this incredibly tricky act of creation.
What were you thinking, you useless creature?
Of course, the truth - as is often the case - lies somewhere in between. Your work is neither as bad as you thought on your worst day, nor as great as you thought on your best.
And there is always something salvageable.
But it is quite difficult to tell yourself that on the days when the doubts come calling, when you realise that your characters are wooden and badly-drawn, that the chapter on which your entire story hangs is filled with out-of-character ranting (or at least, it would be out of character if the person doing the ranting had any character).
The thing is, however, that nothing is unsalvageable. The likelihood is that the terrible chapter still has some good bits in it.
The likelihood is that you know exactly what your characters are like; you just need to re-draw them a little so that they are brought out for the audience. Give them something to do to prove that they are who they should be.
OK, that won't always be the case, but whether it is or not, you know.
So when the doubts come, what do you do? Throw it all away and say "I can't do this"?
You can't though; it's what you are. You do what has to be done; you're a writer, and it's in the job description.
And write, and write and write.
And then go back and re-read it and if it doesn't work, you do it all over again.
It's not easy; it's soul-destroying to have to trash work that took you weeks to create, but if it's actual Trash, then that's what you have to do.
And start again and keep going.
In the book "Into Thin Air" (excellent book, by the way), Jo(h?)n Krakauer describes the "Dead Zone" as you approach the summit of Mount Everest. Because of the lack of oxygen, your body can't process food or nutrients of any sort, so it begins to break down its own muscle and organs to feed itself.
The brain can't function properly and it is practically impossible to perform any acts of rational thought.
Instead, it is the only thing that a climber's feet can do to Keep On Walking. Keep putting one foot in front of another until you get to the top, then turn around and do it in the other direction.
If you do that, if you keep putting one foot in front of the other, even if you can't really see the top of Mount Everest; even if you don't really know what you're doing; even if your body is devouring itself as you climb; if you keep doing it, then you'll make it to the top of the world and - hopefully - back again.
Hopefully as a metaphor it's not too laboured, but I like it, and it keeps me going when I don't know where the hell I am or why I bother.