I'm guessing most writers are like me: when we write, we live for that "Ah-ha" moment. That time when something in our story clicks to bring the story new meaning, or make it bigger/better. You might have your own definition of your "Ah-ha" moment, but for all writers, it's a wonderful thing. Your subconscious just saved your bacon (even if you didn't realize it needed saving).
Honestly, since I plot so heavily before I even attempt my 1st draft (heck, my outline could probably be called my 1st draft), I don't get the "Ah-ha" moment all that often. I know where I'm going, and I know how I want to get there. It's simply a matter of filling in the blanks. My "Ah-ha" moments come before I really start--so that's the hook of the story; so that's how I want to end it; so that's the villain's master plan; etc. It works well for me, and when I start plotting, I can usually chug along pretty well without huge surprises.
Which makes days like today especially worthwhile. I'm almost done plotting the second book in my modern fantasy trilogy (the first one should be available sometime in the beginning of 2013 thanks to Hunt Press), and I know how it's going to end. I'm just filling in a few more blanks to get there. As I was plotting today, I started on the final climactic battle, and my blood ran cold. What the heck? I hadn't done anything I hadn't planned on. And then it dawned on me (my subconscious mind decided to finally spill the beans): a horrific event to my two main characters was about to happen. No, I told myself. That can't happen. What does it mean to the rest of this book and to book 3? And then it dawned on me: Ah-ha! It means much despair and hardship for the two main characters, plus it makes the ending to this book much more believable. Ah-ha!
I think if my subconscious hadn't spoken up, I would have still had a great, compelling ending that led well into book 3. But now I have something even better. So what I'm saying is listen to your subconscious, you muse, as some writers like to say. It'll likely take your story in a way you hadn't anticipated, but that's great. If the subconscious mind thinks it's a great idea, you should probably listen; it likely would have buried it in a corner of your mind where you never would have seen it if it wasn't any good. And just for the fun of it (I know it was great fun for me today), when this happens to you, say it out loud: Ah-ha! Happy writing, everyone!