I have been through the middle of my manuscript about, oh, twenty times. I've done four complete revisions of the material in the middle.
So I think I'm doing my last major fix-up, right? After this, it'll be a word here or there (on every single page, but that's par for the course). And then...
I get to the first big love scene and I realize...it does not belong where I have it.
The relationship really hasn't progressed to that level of emotional intimacy that physical intimacy seems appropriate for these characters.
Oh. My. Word.
It must be moved.
The first question is, where? I go ahead, and find a much better spot. A few chapters later (yep, that far ahead). But at least I can salvage those pages, or at least most of them.
However, that also means that from the point where the love scene originally was to its new "home," I must tweak and/or change my hero and heroine's emotional state and reactions, especially every time they are alone together. They haven't made love; they're still waiting for that.
Oh. My. Word.
I also have another three small scenes that don't fit where I've got them. But these are more independent sub-plot scenes. They won't impact the main plot until near the end of the book, so it's not nearly as big a headache to move them.
Of course, if I'd gotten it right the first few times, I wouldn't have this problem now. But I didn't see it before.
This is something that can be difficult to explain to people who only write one draft. Or to people who don't write. But there it is. I thought I had it right and...I didn't.