Most aspiring writers think they know what a story is, and yet if you ask them to tell you what their story is about, they might say something like this: In eighteenth century England, a young girl escapes her domineering father and stows away on a ship which is commandeered by pirates. She becomes a pirate herself.
Is that a story? Not really. It is the idea for a story.
Something I have recently re-discovered in my never-ending quest to uncover the secrets to writing a "Bestseller" is that you cannot know what your story is about - you can't even begin to write it - if you don't know how it ends. Yes. That's right. You must know how it ends. If you don't know how it ends before you write your story, how can you know what events are needed to get to that end? How will your story make sense? Your story must have a logic to it. Even if it's science fiction or fantasy, it must follow the rules of the world you create. But maybe the most important question is: How will you know what to foreshadow? Foreshadowing is one of the most effective techniques for creating suspense. Without suspense, your story will fall flat.
I know, Stephen King doesn't write that way. In his book ON WRITING, he claims to be an intuitive writer and that's great. If only we were all like that. "If I'm not able to guess with any accuracy how the damned thing is going to turn out," King says, "I can be pretty sure of keeping the reader in a state of page-turning anxiety." But remember, he is Stephen King. Most of us need to know the ending first in order to create the same effect.