I've missed more than 9000 shots in my career. I've lost almost 300 games. 26 times, I've been trusted to take the game winning shot and missed. I've failed over and over and over again in my life. And that is why I succeed.
Man, unlike anything organic or inorganic in the universe, grows beyond his work, walks up the stairs of his concepts, emerges ahead of his accomplishments.
Abandon the idea that you are ever going to finish. Lose track of the 400 pages and write just one page a day, it helps. Then when it gets finished, you are always surprised.