On the basis of his scientific work Lewin (1935) postulated that human behavior is a function of person and environment (B= f (P,U)). The concept of person includes the various biological and psychological characteristics of a human being. A human can only perceive and process certain impulses due to the performance capacity of his brain and sense organs. As a result of personal interests he will also certainly often only seek certain impulses (for example, items of information) and/or will assess these on the basis of his experiences and expectations. A person’s behavior will also be determined by the environment, not just by these characteristics. For example, a shopping mall’s presentation and the presentation of goods have an influence on purchase behavior. This influence is however not the same with everyone. Some people’s purchase behavior will be more strongly influenced than others by such environmental conditions. Many of these aspects are dealt with in this book1 and so at this juncture we will concentrate exclusively on personality envisioned as a characteristic of people (or of a person).