Whatever you want to call it, it's hard.
I am currently working on two books that I finished last year. In my mind, they were finished and just needed a little polishing. Then I went back and read them. Of course, I found stuff I wanted to change. At first, it was small stuff, a word here and a word there. Then I decided to change one of the major characters. I only wanted to change one thing about her, and I didn't think it would be a big deal. WRONG! Changing one small fact about this girl threw off the whole story. I found place after place that I needed to redo or get rid of completely. After a while I had to admit that I totally screwed up my story. It is a big mess now.
So what do I do? I've considered changing her back to the way she was, but it wasn't working. I thought about trashing the whole book and starting over, but that seems a bit excessive.
My books are incredibly complicated. There are several characters, plot twists, pieces that interlock so well that if I change something the whole house of cards topples over. I was wondering about other writers. When you finish a book and go back to revise, do you have this problem? Or are you usually lucky enough to have a good book that just needs polishing?