In certain ways everyone is a psychologist. This does not mean that everyone has been formally trained to study and be trained in psychology. People have common sense views of the world, of other people and themselves. These common sense views may come from personal experience, from our upbringing as a child and through culture etc. People have common-sense views about the causes of their own and other people’s behavior, and personality characteristics they and others posses, about what other people should do, how to bring up your children, and many, many more aspects of psychology.
The informal psychologists’ acquires common-sense knowledge in a rather subjective (i.e. unreliable) and anecdotal way. Common-sense views about people are rarely based on systematic (i.e. logical) evidence, and are sometimes based on a single experience or observation. Racial or religious prejudices may reflect what seems like common sense within a group of people. However, prejudicial beliefs rarely stand up to what is actually the case.
Common sense, then, is something which everybody uses in their day-to-day lives, guides decisions and influences how we interact with one another. But because it is not based on systematic evidence, or derived from scientific enquiry, it may be misleading and lead to one group of people treating others unfairly and in a discriminatory way.