A sample (of the lengthy but compelling piece):
Somewhere in those several hours you will hopefully write something. Unless you're already an A-list writer who can pull advances in excess of $50,000, you'd better either pump out an average of 1000 finished (polished, edited) words of prose per working day, or go looking for a day job. There are roughly 250 working days in a year (I'm assuming you take a couple of days a week off, and have vacations and sick leave), so that's 250,000 words, which is about two ordinary-length novels and a couple of short stories. Some writers do a whole lot more than 1000 finished words per day; some do fewer. If you do fewer and you're at the low-to-middling end of the pecking order, you will not be able to earn a living at this career. Many writers do 250,000 words a year and still can't make a living. They may have part-time jobs, to make ends meet, or a full-time job and do the writing thing in the evenings and at weekends. It's a treadmill.So, uh, yeah. Enjoy!
In addition to writing you will:
pore over copy-edited manuscripts, correcting editorial mark-ups
grovel over galley proofs, looking for typos
keep track of your expenses and petty cash and do all the 1001 things that any small business person has to do to keep HM Revenue and Customs off your back
enthusiastically deal with the press and interviewers, no matter how small or obscure the outlet — publicity is always a priority unless you're big enough to hire a PR manager
deal with correspondence to your editor(s) and agent in a prompt, professional manner because if you ever get yourself a reputation for being difficult to work with you are so screwed ... (luckily editors and agents know that only lunatics and eccentrics want to be full-time writers, so no small amount of their time is dedicated to insulating you from the demands of other publishing folks, and vice versa)
persuade your bank to accept cheques drawn on currencies they've never heard of
learn more than you ever wanted to know about international double taxation treaties and the associated exemption forms
answer your fan mail (if you're lucky enough to have fans)
did I say "write" often enough? I meant "write, even when you're sick to the back teeth of it, when the current project is an interminable drag, when you can't even remember why you ever agreed to write this bloody stupid book, when your hands ache from RSI and your cat's forgotten who you are and your spouse is filing for divorce on grounds of neglect".
And that's just for starters.
(He does admit that there are positive aspects; you're doing what you love, for one, and its one of the few jobs where it's advisable to structure your work life around your social life, rather than the other way around. But it's not easy.)
Edit: Even if you don't want to read the entry, you MUST all read the comments. Everything from an embittered game designer to rants about the value of MBAs to wedding photography to S.M. Stirling being, well, S.M. Stirling. Anybody who remembers what Usenet used to be like will know what an entertaining show THAT is.
Gotta say: I really miss having incredibly long, intense, interesting comment threads like that. I should see if the old YACCS account is still up.