I think we just get so eager to start writing that we don't want to take time to plan, but the eagerness sometimes dries up before the writing has finished. I read about a strategy one writer has. She has a story bag into which she drops her notes for stories. It can be plot points, bits of dialogue, a scene description, or just a general note to herself, but they all go into her story bag. Then, when she is ready, she takes out the various bits and sorts them out and says that she finds the story take shape in all of these bits and parts. Now for the people who start on page 1 and write until the end, this method wouldn't work; but I am more of a quilt writer and I can see the logic behind taking the bits and pieces and patching them together. The point is...no system is wrong if it works for you. :)