They always say to keep a notebook around. This is not only good advice, it is essential. Inspiration does not strike that often. When it comes, you need to have something to catch it with.
Take Joseph Heller. He told Rolling Stone that he got the idea for Catch-22 in the middle of the night:
It kind of burst into my mind. I was actually pacing the floor at four in the morning. I couldn’t wait to get into my office at this small advertising agency and scribble the first chapter.
He wasted no time. If he had waited, we might have lost one of the greatest books of the 20th century.
However, when answering whether writing classes are worthwhile, he digresses into how long it takes to write a book.
There was for me. None at all, I’d say, for the student who lacks talent. You can’t teach talent. And you can’t give intelligence. You can’t teach a person to be funny. A novel takes two or three years to write. By the time a student is halfway through his book, he’ll know so much more about writing and about literature, and will have experienced so much more as a person, that there’s a good chance he’ll lose interest in the book before it’s finished.
This is not much talked about but there are plenty of writers who have gotten a good distance into a long-term project and then lost any interest in finishing it. Of course by then, they’ve committed so much time (or, if they’re lucky, were paid an advance) that there is nothing for it but to press on.
So when you know what you want to write, do it. Fast.
That’s what Heller would have said. Of course, in the twenty years between his debut Catch-22 and this 1981 interview, he had only managed to produce a total of three novels. So, as in so much of life, do as the man says, not as he does.