Four things done well, three done badly. It gets a six.

Done well

1. The definition work in the first chapter. Introversion is separated from shyness and from social anxiety inside about six pages, and the separation holds for the rest of the book, which is rarer than it sounds.
2. The business school reporting. Named people, rooms she actually sat in, quotes long enough to be fair to the person saying them.
3. The high-reactive infant research is explained well enough that I could repeat it accurately to a colleague a week later without checking. Three yellow tabs, close together.
4. The chapter on couples where one partner is which. Practical, specific, and I've used it twice. My husband hasn't read it and does not appear to need to.

Done badly

1. Around a third of the length is the same argument with fresh anecdotes laid over it. I counted eleven separate stories whose only job is to establish that a quiet person did something impressive.
2. Evidence quality moves without warning. A twin study and a magazine profile carry equal weight on a single page and the reader is never told which is which.
3. It flatters me. I'm precisely the audience, the book knows it, and by the end I caught myself agreeing without checking anything. That's the reason for a six instead of an eight, and the fault is at least half mine.