Here comes David Mamet. He is definitely that kind of friend. He can be a bit more bothersome because he is highly accomplished and respected, so he tends to approach everything from the position of "I must be right because I'm more accomplished and respected," and that can undoubtedly be tiresome.
But he is smart, he is not a liar, and he is passionate about his subject matter. It is obvious that he cares. Since he is smart and accomplished, and by this point, he has probably made a lot of money, there is no need for him to write this book except that he truly gives a damn. And it is that aspect of his writing that is most prominent in "True and False." His commitment to the state of the craft is palpable.
None of that means you have to agree with him. I don't agree with him through at least half of the book. Maybe even more. But when I don't, I have to think very carefully about why I don't and make sure that what I think instead is, in fact, a better idea or a better way of doing things.
And then the inherent challenge is that I have to go out there and actually do it. That challenge alone is what makes this book not just excellent but also necessary.