I have a continuing love-hate relationship with short stories. Whenever I read a great short story, or an anthology of great short stories (such as Magic Dirt, by Sean Williams, which I recently finished) I get all fired up and motivated and I sit down and try and write my own. And even though I've been lucky enough to have a few published, writing them is still hard, even harder than writing novels (and that's truly saying something).
The main battle I have with short stories it not coming up with an idea, or characters, or a catchy opening line (although these are difficult too). What I struggle with most is how to actually end them. There's been a few times now when I've let other people review something I've written and they've commented on how much they've enjoyed it right up to the last paragraph when the whole thing has gone to hell in a hand basket. The usual comment is that it has wrapped up too quickly, without tying up loose ends, and in a way that has left the reader completely unsatisfied, even a bit cheated. And the worst bit is these comments never come as a surprise to me, because most times when I wrote the stories I was painfully aware that the ending was sub-par, but I just couldn't think of anything better.
Having said that, I think with practice I'm getting a little better. One of the main things I've learned as I've gone along is that when you strip it down to its bare bones a short story, like any story, is a journey. A character starts at A and ends up at B, and this isn't necessarily a geographical thing, more a change of state from beginning to end. It isn't even always a positive thing: the character or characters can end up in a much worse place by the end of a story than they were at the beginning. The important thing is meaningful movement, and it's this meaningful movement that gives the reader satisfaction in reading the story.
But putting this journey on the page is not always easy. Sometimes it's straight forward -- a character starts the story as a poor beggar and ends as a king, for example. But most times the journey is more subtle, more internal. What happens to a character inwardly is just as important as what changes might occur in their circumstances, even more so in some cases. A character might learn to face some deeply hidden fear, or see some long hidden truth, or understand something much better than they've ever done before. And that's just as satisfying to a reader, because as readers we're joining the protagonist on the journey.
And if the author has made us care about the character enough, in some sense their journey is our journey, and we end up in the same place they do. For me, when I read the best short-stories out there, the ones that have won awards and been reprinted many times, that's exactly what they do for me. And that's what I'm aiming for in my own stories -- not just the short ones, mind you. The long ones too.