1) The prefect has always abused his power over a student, causing the student to develop a schema disliking all prefects. The prefect shows in-group bias by thinking prefects are superior to other students.
2) One day, the prefect accidentally spills ink but leaves without cleaning it. He is not worried about getting in trouble due to optimistic bias, while the students are nervous.
3) When the teacher wrongly blames the students due to confirmation bias, the biased perception is difficult to change despite evidence otherwise.