Why was every volunteer assigned the teacher role in the Milgram experiment?

In the Milgram experiment, the assignment of roles was not truly random despite what the volunteers were told. To ensure the study could effectively measure obedience to authority, the researchers fixed the selection process so that every volunteer participant was assigned the role of the teacher, while the actors were assigned the role of the learner.1

By controlling this assignment, Stanley Milgram ensured that the actual subjects of the study were always the ones placed in the position of administering the electric shocks. This deception was central to his research design, which aimed to test how individuals would respond to instructions to harm another person under the pressure of an authority figure. Today, such methods are widely considered unethical due to the lack of informed consent and the significant psychological distress caused to participants.1