I guess I could argue it was bayes-like reasoning, but no real math was involved. The main info you have are past sales plus a hunch about how this new book might do. The second thing is vague enough that trying to actually run an equation probably would be a waste of time?

Business leans on hunches more than any probably realizes.

Anyways, the real point is the dispassionate interrogations of your hunches and confidences in them. "I think this book will do 10% better than my previous and I would be willing to bet $250 on that" is a lot different from "I think this book will do great!".

Yes, or for that matter "I'd better order none, because I suck" which is a comparably bad choice.

I really think on some level ALL of this stuff is just to remind you that your brain tends to think either it'll be huge or fail, whereas reality almost always serves up something in the middle.