> reading it, I felt like a child: it only says common sense stuff, but I had been doing everything wrong my whole life

Negotiation is a grammar. The rules of the grammar, when laid out on the page, sound incredibly basic. But like any grammar, anyone used to "hearing" the grammar, it becomes immediately apparently who has command of the grammar and who is making grammatical mistakes.

But the point of the grammar is not to learn the grammar, the point of the grammar is to make beautiful sentences. How far you choose to go down the path is up to your own avocation but learning the grammar allows you to understand and communicate the beautiful sentences of negotiation.