An SF writer said,
The cat sat on the mat is not a story; the cat sat on the other cat’s mat is a story
Was it Ray Bradbury? I can’t remember. If you can, help me out of my misery.
In any case, he’s right. A short story is not a situation, not even an event. A short story is a change, a discovery, a revelation.
What’s going to be revealed in your story?
This is a story about a girl who can fly – is not a story. It’s a situation. Presumably early in the piece, we’re shown this girl can fly. And then? What happens then? The fact that she can fly needs to lead to something, needs to help solve a problem, or maybe the girl has a problem because she can fly.
Alternatively: this is a story about a girl who finds out she can fly – is also a story. The girl will start off noticing some weird thing, and weirdness will get worse until the revelation at the end: Hey, I can fly!
So – what about your stories? What elements are setting and situation, givens that are revealed close to the beginning of the story, and which elements are true plot bunnies, discoveries that will change the situation, that will change your characters’ lives?
Must Use Bigger Elephants 
I think that short stories are true idea fiction and you need a twist at the end to make them worthwhile. In that sense they are much harder to write than novels, which can be simple quests.
Strangely enough, I think you’re right. Short stories require much more careful plotting. With novels, you can get away with shit plotting if you’ve invested heavily in characters, but on the other hand, imagine what you could do if you had both interesting characters AND a solid plot.
The fact that you do tend to spend more time along the journey with your characters in a novel is a poor excuse not to do some solid plotting. Yet, this is what tends to happen.
I think it was Bradbury. And you are right. I’ve watched a few movies that start out with a great situation. Then something messes it up and I am at first annoyed, but then I realize something HAS to happen, or in five more minutes I would lose interest!
John Le Carré, according to several people who seem quite sure about it.