One thing not mentioned in the article: People may be wondering how this book became so popular, basically it's because it became intimately tied to the MLM movement, Amway specifically but it did spread beyond that. People at the top of the pyramids would buy thousands of copies to send down their "downline" as part of a motivational tool. The primary goal of someone near the top of an MLM is to convince everyone down the line that you are ripping off that it's their fault for not hustling hard enough, and this book was and is one of the popular ways of doing that.