I first read this book after I had already familiarized myself with Isabel Briggs Myers' work. The constructs that Keirsey invented -- most notably, the temperament groups SP, NF, NT and SJ -- are a very helpful expansion of the MBTI theoretical base. I believe Keirsey's portrait of an ISTP is the finest summary I have ever read for that type. It fits my brother to a "T". I identify most strongly with the ISFP, and Keirsey's characterization of that type is surely the most flattering ever penned. Though some will not agree with Keirsey's speculations about the temperaments of long-dead historical figures, there is much to admire about this volume. I did feel that the book is quite verbose, and needed stronger editing, but this complaint didn't detract from my enjoyment of Please Understand Me. This book will help you figure out so many people in your life. Read it!