From the opening to Those Extraordinary Twins
A man who is born with the novel-writing gift has a troublesome time of it when he tries to build a novel. I know this from experience. He has no clear idea of his story; in fact he has no story. He merely has some people in his mind, and an incident or two, also a locality, and he trusts that he can plunge those people into those incidents with interesting results.
So he goes to work. To write a novel? No---that is a thought which comes later; in the beginning he is only proposing to tell a little tale; a very little tale; a six-page tale. But as it is a tale which he is not acquainted with, and can only find out what it is by listening as it goes along telling itself, it is more than apt to go on and on and on till it spreads itself into a book.
I know about this, because it has happened to me so many times.