"But I mean a good marathon time, and getting a book accepted by a publisher, in which there is an advance and royalties (not self-publishing)."

That's too low a bar. If you don't make the New York Times list, you're not really writing a book, and if you're not winning the Boston marathon, you're not marathoning.

Or so some would say.

I guess my point was that success in these things at a reasonable (i.e. definitely not expert) level has far more to do with perseverance than "natural" talent or physiological characteristics - you seemed to be suggesting that the latter has far more to do with it than it really does. Neither of them are out of the normal range of human capability the way, say running a 10s 100m is. People consistently underestimate what they are capable of in these sorts of things.

Ignoring the problems and gatekeeping attendant in publishers, I belive most people could write a book that a significant number of people they didn't already know would pay to read (this may fall well below the numbers that would make a publisher interested). It probably wouldn't be their first book. Similarly most people could run enough to post a decent marathon time - again, probably not on their first marathon.

The main characteristic is not "raw talent" or physiology, respectively - the main characteristic is trying, failing, learning from your errors, trying more.

I forget who said it but "talent is a pursued interest". If you pick a random person and they choose to put the time in odds are extremely good they could write an ok book or post an ok marathon time. They aren't likely to write a best seller or break 2:30 - but that's not the point.

It is undeniably true that the overwhelming majority of people will never do either of these, but that is not because they are incapable of it but because they do not choose to focus time there.

>I belive most people could write a book that a significant number of people they didn't already know would pay to read (this may fall well below the numbers that would make a publisher interested)

What's mostly missing from this discussion is marketing. Sorry, but even pretty good books will languish on Amazon (which is mostly what matters) if you just put a book out there, fiction or non-fiction, with the attitude that "If you build it, they will come." (Like most everything else.)

Unless you're a known quantity for other reasons, even getting accepted by a publisher is a tough slog and there is a long list of stories of publishers (like studios) passing on blockbusters. Not that getting in with a major publisher is any guarantee of success but cultivating a fan base as a total independent self-publishing is that much harder.

(In addition, as someone who does a lot of writing and editing, you're also probably optimistic about the abilities of said random person.)

That’s why I chose “significant number” rather than a sales figure ... the whole commercial aspect is a separable issue, imo.