"One piece of advice which I came upon in texts [on how to sell fiction to pulp magazines] over and over again was the firm suggestion to read the magazines and then write for a specific market. I tried. I tried very hard. But I could not read those stories. I learned that there were some names I could read and enjoy, but I did not want to try to learn to write like those chaps. The rest of the contents of the pulp magazines seemed to me to be such godawful junk, I felt slightly edgy about appearing in the midst of it, and at the same time I felt nervous about my qualifications to be a low-level snob.
"It became my habit to write the story which bobbed up to the surface of my mind when I rolled new paper into the machine, and to write it to whatever length the substance of the story seemed to require. This is a matter of subjective taste. Were ten writers to attempt the same story, the length would vary wildly. Pace is highly individual.
"Once the story was done, I would change hats and become my marketing director. I would write down a list of possible magazines, with the most likely ones at the top of the list. I would write this list on a file card, and then start sending the story out, each time with return postage, until either it sold or the list was exhausted. In 1946 and 1947 there were twenty to thirty stories in the mail at all times. I remember meeting a fellow at that time who had been waiting three months for word on his novel, then in the hands of a large publishing house. While waiting, he was not working. I thought this a most peculiar attitude.
"My work habits accounted, I think, for not only the diversity of plot and structure and societal themes in early work, but also for the diversity of the places where they were published. All manner of pulps except the love pulps and, during 1947 Cosmopolitan, Liberty, Esquire and The Elks Magazine [sic]. When I tried to work exclusively within a specific genre, everything went stale for me. The words died."
--- from "Introduction and Comment," MacDonald's preface to a number of scholarly papers written about his work, published in the Spring 1980 issue of Clues: A Journal of Detection.