In these later chapters of the book, Berners-Lee starts getting into the privacy part of the World Wide Web. Although he's tried to keep the web completely public and believes everyone should have access to it, there are some parts of the internet that should be private/blocked and personal information should be withheld, at least to certain individuals. In the middle paragraph on p. 126, Berners-Lee explains that we should be able to trust people and that it is an essential part to the Web working at its full potential.
Of course though, we are not able to put our full trust into something or someone we don't know such as a certain website or who's behind a website running it. In chapter 11 on most of p. 145 he goes into talking about "cookies" and linking into a person's computer through a website all possibly with or without a consumer's knowledge. Now days most websites just allow cookies to automatically opt-in a consumer without prior warning. Websites do have privacy policies which are generally supposed to inform you of the data they are collecting from you and if it is being sent anywhere, etc. Because privacy policies are usually extremely long, most people don't either have time to read it over or simply don't want too, which companies know. He also noted that in Europe there are strong regulations over consumer privacy but lack such laws in the United States because the government hopes to have "some sort of self-regulation". This is where trust comes into play. Especially in recent years with the Internet becoming an essential part of daily tasks, people don't have time to look into every website they may be using and make a conscious decision whether or not they can trust them.