I do hate feeling the hot breath down my neck. There are two distinct crafts, writing and writing for someone. The second requires a kind of second sight with which I do not seem to be gifted. In writing you put down an idea or a story and then see whether anyone likes it, but in writing for someone you must first, during and after, keep an invisible editor sitting on the typewriter shaking an admonitory finger in your face.
John Steinbeck (1952; from Steinbeck: A Life in Letters, eds. Elaine Steinbeck and Robert Wallsten; New York, Viking, 1975).
I could not have ever hoped to have said it better myself.