I have an odd problem. I love to write. In fact, I've written many, many short stories. Most of these are, well, erotic, but they're still stories. I like to go through my day, think of an idea and then jump on my computer and add that idea to whichever story it happens to match up with. My problem is writing long stories. I've always wanted to write a full length book, but whenever I sit down to write I get bored with the story after a page or two. I write because I enjoy it, so when the story isn't very interesting I have no desire to continue writing. I know that a good book needs a solid plot, but I can't write to an end goal with that in mind. My writing is entirely based on the current position of the story; if my characters are at a crossroads, instead of taking the road that leads to the destination I set out beforehand, I'd rather take the one that seems the most interesting at the time, regardless of its relevance to the overall story. So, my question: what can I do to have a good plot with a word-by-word writing style instead of a pre-planned ending?