A good starting point for understanding Fitzgerald is a passage from his 1933 essay “One Hundred False Starts”:

Initially, this seems a rather defensive rebuttal to charges that Fitzgerald's interests were narrow and repetitive. Yet the real concern is not his supposed lack of range (an accusation most writers suffer) but the pressures of earning a living. “For eighteen years,” the author insists, “writing has been my chief interest in life, and I am in every sense a professional” (Afternoon of an Author 131). While that description may not jibe with his image, it is important to remember that he was the only major author of the 1920s other than Sinclair Lewis (1885–1951) to live exclusively by writing. Financial considerations dictated that few artistic choices were made without considering the marketplace. And yet Fitzgerald could never view his work objectively as true professionalism demands.