What’s Your Motivation?
Short stories are short, by definition. They’re also easy to unbalance. Here’s an example. You’re writing a mystery. In your first scene, you introduce your sleuth, and he investigates the dead body. Magic: your mystery is on track. The following scenes will include misdirection, red herrings, and clues.
Somewhere in there, you need to do a little characterization. You give your sleuth a toddler. As kids will, the kid takes over. Before you know it, the first draft of well-planned story isn’t a mystery. It’s a story about a single father who just happens to be a detective.