I couldn't make this one up if I wanted to. I've been studying for my PMP, not because I want to be one, but because I want to understand that side of things a bit more and be able to talk the talk when it's advantageous, and this is one of the first things I learned while reading the Project Manager's Book of Knowledge. That in the fourth edition they've added interpersonal skills, but relegated them as add-on material in an appendix. If you teach people that people are an afterthought in their study material, there's the real possibility they'll consider people an afterthought in real life. Or at least that they'll consider considering people as part of project responsibilities as an afterthought.
Title: Appendix? Snarky: The PMP prepared me for our one on ones. The appendix to the fourth edition had extensive information on necessary interpersonal skills.