I found the textbook example interesting, where the co-author with experience thought it would take 7+ years, and everyone else thought it would take about 2.

I found the textbook example interesting, where the co-author with experience thought it would take 7+ years, and everyone else thought it would take about 2. That makes a lot of sense to me, because I wrote a textbook in about 2 years. But... There are textbooks and there are textbooks. My book covers exactly what I need for my class, has no publisher (students download it from the class website), and doesn't have a lot of the bells and whistles that a publisher would demand. I can easily see how a "real" textbook would take over 3x as long. So part of the lesson of the authors' textbook is a standard software development lesson - there's a huge gap between a working prototype and a shipping product, and even if that prototype does everything you think the product needs to do, (a) you're wrong, and (b) you may be less than halfway to the point where you can ship.