I have just found this excellent description of how it feels to start writing a book:
"A book unwritten is a delightful universe of infinite possibilities. Set down one word, however, and immediately it becomes earthbound. Set down one sentence and it's halfway to being just like every other bloody book." (The Ghost, by Robert Harris.)
This rang so many bells with me, and more or less sums up the huge dificulty I at least have in getting going. Because once the book has been started, it can never really come up to that perfect dream in the writer's head.
Or can it?