Do it with no hopes of ever making a living at it.
An artist is a creature driven by demons. He don’t know why they choose him and he’s usually too busy to wonder why. He is completely amoral in that he will rob, borrow, beg, or steal from anybody and everybody to get the work done. The writer’s only responsibility is to his art. He will be completely ruthless if he is a good one. He has a dream. It anguishes him so much he must get rid of it. He has no peace until then. Everything goes by the board: honor, pride, decency, security, happiness, all, to get the book written. If a writer has to rob his mother, he will not hesitate; the “Ode on a Grecian Urn” is worth any number of old ladies.