We learned about these things through research. Someone somewhere did a study and found each of the above findings. Who knows, maybe they did the Croissanwich study at Burger King one morning and asked people which sandwich they preferred. The fact that the participants had already gone to Burger King for breakfast meant that they had at least some tolerance for Croissanwiches. When we ask questions like these, we are questioning the methods the researchers employed in their studies.
Research methods are a variety of techniques that people use when studying a given phenomenon.
They are planned, scientific, and value-neutral. Instead, they are deliberately employed in a way that is designed to maximize the accuracy of the results. Assume, for example, that you want to do a survey to assess students' level of satisfaction with the parking situation on your campus. Because no one wants to take time to be interviewed, you are forced to start interviewing the people sitting in their cars waiting for parking places. Since they're bored anyway and have nothing better to do, they agree to answer your questions.