The moment we see something we instantly judge whether it is positive or negative. We do this all the time, automatically and preconsciously, to everything around us.
All input is directly classified as either good or bad. Whether we appreciate specific input as really good or good (or really bad or just bad) does not really matter for this classification.
This has enormous implications. If you want it or not, everybody you encounter is immediately classified as either good or bad. The impact on your subsequent judgments is huge, and this influences how you behave towards a person or object.
Most people want to be unprejudiced about differences in race, age, or employment. The problem with automatic judgments is that they are not based on what we want to think, but on what we have experienced over and over again. All the negative news in newspapers, all the jokes and remarks made by people around you: they all weigh in on your experience. This means that we cannot escape having stereotypes about most people.