Epiphanies are dangerous.
Here you are, writing a book, blissfully unaware of what's about to hit you. And then it hits you. Either because you've done enough of something to see a pattern, or because you've read another book that has shown it to you. And suddenly you want to rewrite everything you've written so far, to apply this new knowledge.
But you can't. You're too far into the story. It's locked. Rewriting it fully will mean discarding it completely. And so the battle begins.
So you finish this book? Do you abandon it and start a new one? Do you continue writing it, ignoring what you have glimpsed and sticking to the original story?
That's where I'm at in my current novel, The Badlings. I have learned so many things, primarily about plotting, but it's too late to apply them. So I have to suck it up and finish. 8 chapters left, and then I can move on to the next book and use my insights there. Can't wait. Can't bloody wait. 8 more days, folks, 8 more days and I will be done.