"It's also best to be female, educated and in your early 40s: the survey's "top earners" -- those who indicated they could live exclusively off their earnings -- were 68% female, and 33% had a degree, compared to an average of 28%. High earners also dedicated more of their time to their writing, churning out 2,047 words a day on average, as compared to 1,557 for the rest of the sample."
And this thread on the kboards really rams home the need for speed. Writing is just like The Fast and the Furious, just without Vin Diesel or cars or chases or explosions and a lot more typing:
…In order to do this work, you must be fast. I say that at a minimum, you want to be doing 2-3k words of nearly publishable fiction per day, five days a week. That gives you the ability to churn out 10-15k words a week, and so you're getting out a short book a month, or perhaps a few shorter serialized books a month."
The writer, who goes by the handle Gorvnice, makes some very good points about how to write for a living. It's both sobering and inspirational stuff.