“WD: You’re terribly prolific, but a lot of writers produce one book in a lifetime. Would you advise young writers to spend all their time polishing one piece or to go for quantity?
BRADBURY: It simply follows that quantity produces quality. Only if you do a lot will you ever be any good. If you do very little, you’ll never have quality of idea or quality of output. The excitement and creativity comes from a whole lot of doing; hoping you’ll suddenly be struck by lightning. If you only write a few things, you’re doomed. The history of literature is the history of prolific people. I always say to students, give me four pages a day, every day. That’s three or four hundred thousand words a year. Most of that will be bilge, but the rest … It will save your life!”
I came across this quote used in Quantity Produces Quality – A NaNoWriMo Post. The interview excerpt is from a February 1976 Writer’s Digest interview with science-fiction writer Ray Bradbury.