The easiest part of writing a book is starting it. It's like the beginning of a new relationship. I get an idea and for weeks I play around with it in my head, imagining all the possibilities, the various directions it could go in. I make a few brief notes. I invent characters. I give them names. I decide on a starting place. I place my main character in a room, a street, a car. I give them thoughts and opinions and memories with which I start to build up the beginning of a story which I intend to slowly unwind.
Then I start. The first few pages are delicious. I can hint at any future plot, I can excite, I can promise the earth.
The next chapters are enjoyable. I'm building things slowly, getting to know my story, filling in bits of background, finding out stuff about my characters that I didn't know. It's good, it's fulfilling.
Then the low period starts. I know these characters and I know their story and I'm growing a bit bored with the whole situation. The passion is waning and I'm on the brink of arguing with every twist and turn. At one point, about two thirds of the way through the book I want out. I want a separation, maybe even a divorce. It's too complicated, it's unconvincing, it's dreary.
New ideas for other books tempt me. They call me away from this tome. Start something else they say but I stick with it for better or for worse.
Then it's finished and I have this sadness. But hey! There's another new book round the corner. The thrill of the chase, the delight at the commission, the beginning of another love affair.