Have you ever tried writing completely different chapters to see where your novel/story is heading? I'm about 3/4 of the way through a first draft of a novel (at about 65,000 words) and I have just completed one chapter that is left kind of open-ended. The next chapter could take the novel in any number of directions. I have several options in mind and have started one today, but I was thinking of starting another chapter in exactly the same place to see where that could take us too. I have a pretty clear idea of the the ending, I'm just working out the middle right now.
Save it in the computer as version 1 and version 2. When you find yourself working on one version more than the other you'll know what's right.
On an old and now long discarded draft, I wrote three versions of chapter one. While each had the same beginning, they each ended differently. I don't think it's uncommon to try different ideas and branch out the story or see where the plot can go. After all, as @Paneera said, you might find a piece that fits well with your story.
Not exactly, but several times I've jumped back to insert something, and it spiraled off in a completely different direction, rendering what I had useless. Of course I wouldn't keep it unless it were an improvement, but it usually is.