Writing for fun and profit. Or at least for fun.
"I have always believed that advertising is the second most profitable form of writing. The first, of course, is ransom notes." That line was written, you might have guessed, by an ad man. As someone who spent far too many years "rattling a stick in a swill bucket" (George Orwell), I have to say that the guy has a point.
Writing is not the easiest way to make a living. Fashions come and go, very few people manage to sustain a decent career over time, and if you haven't had the foresight to write a timeless bestseller, there's no such thing as a pension (though if you bought one of the first 300 Harry Potter hardbacks intended for library use, you could flog it on e-bay -- there's one listed now for £17,495. Not really enough to retire on.)
Mark Haddon said that he was wallpapering the walls with money after writing Curious Incident of the Dog in the Nighttime, but that's fairly unusual. I suspect Philip Pullman had a similar experience. And Stephenie Meyer. But most writers are not rich. Even most well-known writers are not rich. According to the official UK Graduate Careers website:
The annual average income for professional writers aged 25-34 from writing alone is only £5,000. Approximately 60% of all writers have a second job. Only 20% of writers earn their income exclusively from writing.
But, you cry, if only I could sell the film rights I really would be rich! Last I heard, film rights for novels that weren't massive bestsellers were selling for a few thousand pounds. Which is nice. But not enough to move to Biarritz. (Even the film rights to Harry Potter -- all seven books -- didn't sell for much more than £50,000.)
The only sensible course of action is to stay calm and recognize that writing is a long game. Turning out a book a year till you drop dead means writing a lot of books. And the best way to survive the realisation that your current book is not going to sell millions of copies is to write another book.
An alternative career (like a spouse with a proper job) also comes in handy.
Having said all of that, writing for fun and profit beats the hell out of selling washing powder. (This links to one of my immortal Persil commercials. The voice of the alien is also me, and if you can guess which fairly famous UK actress voiced the woman, you are an actual genius.)