Yes, you need to be able to have a means of living in order to write. Selling your books is one such way, but not the only one. Lots of writers would still write without a business model.
That was my only point, really. It's false that one would have to be "insane" in order to write. We can argue about ifs and buts all day long, but that bit which I was replying to was hyperbolic and false.
"Painting. Sculpture. Composing. Singing. Acting. The playing of a musical instrument. Writing. Enough books have been written on these seven subjects alone to sink a fleet of luxury liners. And the only thing we seem to be able to agree upon about them is this: that those who practise these arts honestly would continue to practise them even if they were not paid for their efforts; even if their efforts were criticized or even reviled; even on pain of imprisonment or death."
He struck gold, of course, but note the sentiment he expressed. By his own admission, had he never been paid for it, he would have kept writing anyway, because that's what he does. And when he was starting he had other jobs -- and a family to support -- and really struggled with money, but kept going anyway.
Second, as has been mentioned to you in another comment, mastery is not directly related to having been paid for your art. There are acknowledged poets whose work was published posthumously. They didn't live off it.
(The quote was by Stephen King, by the way. Regardless of what you think about his literary skill, the man sure can speak about writing).
https://www.theguardian.com/education/2001/nov/24/arts.highe...
I don't think anyone suggested that. Society may be better off despite Glass never becoming a professional composer, though.
I meant that, while Glass not becoming a professional composer would have been bad by itself, it may be a reasonable loss compared to the advantages.
But you need an income to be able to write.