How does one go about laying out the plot of a story? It seems I'm able to come up with interesting characters and settings to begin stories but I can never follow up because they're always based off of spur of the moment things. Do you pick some kind of point to express or some kind of goal to be achieved? I've written a few stories but never finished any of them because the plot seems to fall apart near the middle. Any kind of input as to the development of a fantasy plot would be greatly appreciated.