My plans go out the window

I had read somewhere that you need to know where you are headed in your storyline. That way you know when you reach the end. Not only that, you have a direction you need to go in during your journey. For my first book I sat down and religiously worked out a structure for each chapter etc etc etc. It must have taken me three or four days. All the time I had the opening line burning itself into my brain.

Finally I got around to writing. The first line went down onto the fresh blank computer screen and away it went. I use that term quite deliberately. There were times when as I read back over what I had just written I would ask "woah were the heck did that come from?" (or words to that effect)

Within a very short period of time I threw my nice neat, detailed storyline structure out the window and just wrote. The further I got into the story, the more it became painfully obvious to me that the original ending just would not fit. I let it sit for a few days, manuscript untouched.
It was January 26th. We were going out for a celebration dinner for my birthday (remember that folks) As we got into the car the ending came to me like a flash out of the blue. We got home about ten thirty, my wife went to bed, I went to my study.

When I finally climbed into bed it was just after four am and the final four chapters were written.

But then I had a problem. The novel was, for all intents and purposes written, but the story was no where near told and my initial question was no where near being answered to my satisfaction.