I read this book immediately after reading The Silent Language, and it complemented it quite well. Robert Sommer really shows the importance of considering the human aspect, an aspect that is still often an afterthought, when designing buildings. His arguments are focused in space usage and interactions but easily translate to other aspects of design.
He walks us through some distinctly different examples, such as a mental hospital, a bar and a school, to show the breadth of the capabilities of applying this type of research to the design process. One example, from the mental hospital, describes how a ward was beautifully renovated to have a very clean and modern appearance. The chairs, however, had been designed to stay against the wall which supports the clean and orderly look, but unfavorable for conversation between patients, which is the reason the ward exists in the first place.
His final paragraph is a potentially ominous one, claiming that the only universally applicable point he has gathered from all his research about people is that they are extremely adaptable and so in designing new spaces and objects we are really designing humanity.