A set in psychology is a group of thoughts and behaviors that we do in certain situations. When we’re in a certain situation, it’s like a switch gets turned on in our minds. We start to think and act the same way we always have in that situation. For example, when you walk into your classroom you have a certain set of thoughts and behaviors - you sit down, pick up a pencil and open your notebook. That's the set for the classroom, and it’s the same every time you enter the room.