The world is 3 days: As for yesterday, it has vanished along with all that was in it. As for tomorrow, you may never see it. As for today, it is yours, so work on it.
Writing a novel is a terrible experience, during which the hair often falls out and the teeth decay. I'm always irritated by people who imply that writing fiction is an escape from reality. It is a plunge into reality and it's very shocking to the system.