[Finnucane]

>The editor will set the advance so the book never earns out.

Not deliberately, most of the time. If you have a track record, a good agent, and there's a competitive bid for your book, they might overpay knowing that they don't have to earn out to make a profit, they just have to get reasonably close. Maybe they can make it up in subrights. But if those things are not true, the advance will be lower.

[TheOtherHobbes]

Not for fiction. For non-literary (i.e. non-household name, tech-oriented) non-fiction - definitely.

It's a production line, and it's rare for authors to do more than one or two books.

Some bigger publishers really do have spreadsheet models of likely sales, and they base their acceptable advance offers on them.