I touched on this briefly before, but I corresponded back in the pre internet days with what would now be considered a high mid list middle grade and YA author.
They were “big” enough to generally make a living at it, but “small” enough at the time to still handle their own mail. In between the blather I sent, we also talked books. I got my first look at writing as a business. How the size of their market compared to the USA meant a best seller in their home country was only “meh” if the same number sold in the US. (Their home market was only about a tenth the size of the USA market.)
We talked about the creative side, and they had some kind and well intentioned but ultimately incorrect writing advice. But old folks always think us whippersnappers just don’t get it (I’m guilty of that myself, as I hit middle age). Their “incorrectness” was right for the industry at the time, but wrong for our target audience. The industry changed, and I imagine they took the change in stride, forgetting our ephemeral exchanges.
But my biggest take aways were keep writing, learn to write, to read, to edit, and be edited. So I did, taking up industrial writing to pay the bills until I could get back to novelling. Several decades later, lol, but back to it.
We get by in the biz of writing with a little help from our friends. Thanks, friends.