The instruction here is not for every kind of writer - not for the writer of nurse books or thrillers or porno or the cheaper sort of sci-fi - though it is true that what holds for the most serious kind of fiction will generally hold for junk fiction as well. (Not everyone is capable of writing junk fiction: It requires an authentic junk mind. Most creative-writing teachers have had the experience of occasionally helping to produce, by accident, a pornographer. The most elegant techniques in the world, filtered through a junk mind, become elegant junk techniques.)
