I might amend that to say "professional authors sell."

I don't think someone who labors over their darling story for a decade, self-publishes it, and only sells a dozen copies is any less a "real" author than Tom Clancy or Stephen King ... she's just not as professional. Writing to her is a work of love, a hobby, a passion.

She doesn't just sit down at the keyboard and hammer away until she has her thousand words for the day. That's what makes the professionals professional: they see writing as a job.