Writing, like other forms of self-employment, is tough because you can never say you're done. As a teacher I got a degree that said I was "ready" to teach, not that it was even close to the truth. In addition, I had a finite beginning and end to my work day and work year, not that the work really ended at 3:30 or June 1st. There was both a sense that I was on a schedule and a sense that I was qualified for the tasks involved.
Writing has neither clear qualifications nor a definite schedule. A writer may have a degree in medicine, law, journalism, English, auto mechanics, or no degree at all. A writer may work at three in the morning or four in the afternoon. She may scratch away at a legal pad or pound on an old Selectric or peck away at a computer keyboard with two fingers. She may wait years to get published, get lucky early on, or never grasp that elusive brass ring. And she knows in her heart that it's never quite done, this apprenticeship she's taken on.
She can always get better, should always get better. She looks back on her early work and wonders why she didn't see the awful weaknesses: the shifting voices, the bland phrasing, the repetitive description. But then she sees it in the work of others more successful than she and understands that writing is a process that is never perfect. No matter how much fans love a writer's work, that writer is always learning what she doesn't know, what she didn't do that she'd like to improve upon. Heaven help the writer who believes that she's learned everything, because no matter how much commercial success she achieves, she doesn't get what this particular field of self-employment -- dare I say self-fulfillment?-- is all about.