Well, PWS means person who stutters. By giving ourselves a label "stutterer" we unconsciously give ourselves a set of rules that we have to follow (for example, if you associate "stutterer" with someone who has trouble speaking, and usually does not like to communicate with other people, then probably you will follow these rules, that is, you will have trouble speaking, and you will not like to communicate with other people) for the fact that we are "stutterers". It is similar, for example, with doctors - we expect a certain behaviour from them, and if someone mentions the word "doctor" you do not see the individual, but rather a professional that you expect to act a certain way. This idea of labels is not easy to explain, at least for me, but this is the rough idea. Full explanation is in the book.