From a Newsweek interview with Joyce Carol Oates:
Do you ever worry about the sheer volume of your work diluting the impact of any individual book?
I think thatâ€™s inevitable. If one publishes a couple books year, I donâ€™t think one can avoid that. But Iâ€™m not trying to create an image of myself or have a career thatâ€™s necessarily sculpted or guided. Iâ€™m more interested in individual projects. So if I have an idea, I want to execute that idea the best I can. When it becomes published, like â€œRape: A Love Story,â€ it passes over into what we call production. The editors find a cover for it and I work with them with the cover art and the design of the book, which to me is very excited because itâ€™s an aesthetic production. To me it has a luminosity; there can be beauty in the physical look of the book.
(Thanks to Emma for the link.)