I tried making a go of being a professional sf author, albeit through a small press instead of getting a deal with a big corporate press like Tor, Orbit, DAW, Angry Robot, etc. Of course, I didn't quit my day job, so I had TWO full time jobs: software developer AND published author. I had to keep it together at my day job, do my own promotion online (never mind that I was shit at social media), and try to write more books — all at the same time.
Of course, Curiosity Quills Press is dead now (and good riddance; they fucked over a lot of writers in the end) and writing's just a hobby for me again.
I might self-publish in the future, but I might not. I make more money as a developer in a year than most full-time authors make in five, and if a reader finds my fiction online and isn't happy with what they're reading for free, I can tell them I ain't Burger King and that if they want it written their way they'd better write it themselves.
You can't say things like that if you're depending on the goodwill of readers to pay the mortgage, but my day job gives me a limited and somewhat precarious source of fuck you money.
I think a lot depends on 'momentum' or starting from creating no money at the start, and slowly creating a reputation, a fan base, and many other 'boring' things related with being a creator and making a living that could replace that day job.
Working on a 'traditional' job gives us X USD for 160 hours a month of alienated work while creating things takes out money from our pockets for the first, we say, 18 months.
I don't try to oversimplify it, more like understanding what's happening with me.
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