And it's true. (2)
What this means in practical terms is that there is no such thing as good enough for the aspiring writer. Don't aim *for* the target. Aim through the target. Adequacy isn't.
The other thing that it means is that writers, while we are in some respects in competition with each other, are in competition in a funny sort of way. You don't lose readers to another writer the way McDonald's loses customers to Burger King. You lose readers because you aren't giving them what they want, not because somebody else is.
Admittedly, on one level, there are only a certain number of novel slots in a given year. On the other hand, while my readers may have some overlap with, say, autopope's or desperance's or papersky's or truepenny's or naominovik's readers, the fact of the matter is that all those book purchases come out of a discretionary budget. And people do in fact spend the food money on books, if they want the books badly enough. (I've done it.)
So, scott_lynch selling a book does not automatically mean that I will not sell a book. In fact, it may mean, in the long run, if Scott is wildly popular, that there are more readers in the bookstore looking for science fiction and fantasy. And some of them may slop over to me.
It's an ecosystem, in other words.
And so that's one reason why I do the day-in-the-life-of-a-writer blog I do. *g*
(1) The other one was from skzbrust, and it went something like, "It doesn't matter if the first novel you've finished sucks. Because finishing a novel is more that 95% of the people who want to be writers will ever do, and if you have finished one, you can finish two. And the second one may suck less than the first."
(2) In fact, I am reasonably convinced that there is a heck of a lot of room for commercial mediocrity, too.