I am sympathetic to the concept of “mental models.” I believe that models have value in many situations. And so I wanted to like this book. But I can’t. Too many of its examples are trite or obvious. And it contains too many examples of reasoning by metaphor. For example, the concept of critical mass in the context of physics is clearly important and valuable. And, I can see how you can be tempted to apply it to social or economic situations. You can talk about “critical mass” in relation to, for example, new product adoption or a political campaign, but in those contexts you’re talking about quite different phenomena. Talking about “critical mass” is a potentially useful thing in some contexts outside physics as long as you recognize that the connection you’re making is metaphorical and that it may be quite misleading in terms of predicting the future or suggesting action. Too many times in this book the authors seem to ignore factors like this. They may be quite bright and enterprising folks. But, they don’t seem to see that taking concepts for one domain and applying them in another domain has major limitations. The book is not without value. But, let’s all be careful to think critically about stretching metaphors too far.