A few years ago, while I was writing the Disillusionment Series, I set myself up for some misery. It wasn't the same old stare at a blank screen until you bleed misery, no, this was painting myself into a corner. See, I wrote Daughter of Gods, Book One and Starlight and Judgment: Book Three of that series first and went back to write what my daughter called a "bridge" book for Revenge of the Gods: Book Two. The character from Starlight told me what had to happen in Revenge. Writing Revenge should have been easy.
I pounded through the events, wrote it in record time and ended feeling so devastated my only salvation was to escape the grip the story had on me. Doing dishes, gardening, none of it helped much. So I waxed my car. I'm not the strongest person, especially in my arm and shoulder areas, so it was no easy feat to rub the wax on and polish the wax off, and I didn't have a small car, but it was exactly what I needed at that time.
And then readers came at me with "how could you do that" statements. Simple answer, I had no choice. The events had already happened, they had to happen to put that character where she needed to be. Everyone who reads the story knows this, but we all disliked the inevitable-ness anyway.
I'm not sure if other authors get so involved with their characters and stories, but Revenge of the Gods, put me through the ringer and I tell most readers not to read it without jumping right into the third book. I don't usually like to write stories that end so heart wrenching and crushing. Usually the heart wrenching and crushing come in the middle. ;)