We all know the feeling when a daydream turns into something real (whether it be poem, short story, or novel). I think there's a moment, or at least a series of moments where what you're working on becomes more than just a notebook full of words, or a Microsoft document on your desktop. The skeletal story structure gives way to muscles and sinew, until it's a REAL BOY (Pinocchio style).
Suddenly it breathes, it moves, it grows, even lives. It is substance, it has purpose, no matter how much you might have hated or doubted it in the past. And that's when your book turns into Frankenstein's Monster.
So, would be Dr. Frankensteins, the point of this blog post is not to ponder the consequences of creating a living being. Rather, it is to not lose hope, that the moment of "creation" does happen, and when it does, it'll make the hard work worth while.
Just make sure you don't let your little bundle of joy off into the world before its ready. Edit, re-read, and edit again for good measure. But feel free to squee at random moments, because writing a book is an amazing thing.
Revel in it.