Everyone in the world thinks he can write. I think I can write fiction, although it remains to be seen if I am deluded in this. Why have I focused on fiction? I have no interest in delving deep within myself to write autobiography. I suspect that if I were to try to write nonfiction about someone or something I like or care about, it would end up as a sad and turgid recitation of facts. Is my fiction any better?
The proof of the pudding is in the eating. When someone is willing to pay you for your writing, that is an indication of the basic quality of the work. There isn't a direct one to one correlation between money and quality, but no money is pretty much equal to no quality. It's non-linear after that. Once that binary hurdle is crossed, it's hard to measure how "good" your writing is.
Take a blogger who hates his job and uses time on the clock to pour out 3000 blogwords a day on the subject of his choice - wine, shoes, baseball, politics, etc. He says to himself, "Gosh, I really hate my job, but I really love writing my blog. I should try to write for a living instead." There are plenty of examples of people being offered columnist slots on SubjectX.com after having written 500,000 words of cogent commentary on Subject X. But what about fiction?
Even if he's realistic about the fact that it would take years for him to develop his skills, income from writing will never come close to what he makes in his day job. So why bother? Where's the satisfaction of always being a rookie also-ran?