There's something wonderful about being able to write when you know exactly what's going to happen. It allows you to think more about what you're writing now, rather than "where the heck do I go with this next?"
Some would argue that is what plans are for. But for me, I do a first draft which is mostly worry and "good god, what have I done". Then I get to the end, and I rather pleasantly know my characters, and have a plot.
But there's something strange about second drafts. Sometimes, there are big problems in the first draft that have to be corrected. Logically speaking, you don't know if your corrections are going to work - you just know that they're fixing the current problem. How then, is it that the corrections work themselves out? How can removing an entire scene, which would have effected the MC in a variety of ways, and driven the plot in a variety of ways, not actually change the book so much that you end up with another first draft?
This happened to me recently - I realised that I had a scene I didn't need. I cut the scene, wrote some other stuff. Not once was there any guarantee that the other stuff would bring me directly back into the plot line, but it managed to. I've been a little perplexed as to how it worked out so well.
I think it comes from my changing of my MC's main motivation.
At the end of the first draft, I knew my MC and her motivation didn't fit. Her motivation didn't drive her to do what she was doing by the end of the book. So I went and changed it, to fit her actions at the end of the book.
This new motivation not only drives her to those actions in the climax, but keeps her on task for the rest of the plot line. There is no other way she can go, given her circumstances, who she is as a person, and her motivation.
Neat, huh? I was quite pleased with this revelation, and quite heartbroken by the fact it means that I've got to go in search of motivation in another WIP. But this revelation provides a tool for fixing things, and that is always useful.
So when you know how things are going to turn out, and you know who your characters are, make sure their motivations are going to drive them towards the appropriate actions. If they are of a certain character, that character, paired with the right motivation, will keep them on track.