Three persons are involved: the one running the experiment, the subject of the experiment (a volunteer), and a confederate pretending to be a volunteer. These three persons fill three distinct roles: The Experimenter (an authoritative role), The Teacher (a role intended to obey the orders of The Experimenter), and The Learner (the recipient of stimulus from The Teacher). The subject and the actor both drew slips of paper to determine their roles, but unknown to the subject, both slips said "teacher". The actor would always claim to have drawn the slip that read "learner", thus guaranteeing that the subject would always be the "teacher". At this point, the "teacher" and "learner" were separated into different rooms where they could communicate but not see each other...
The "teacher" was given an electric shock from the electro-shock generator as a sample of the shock that the "learner" would supposedly receive during the experiment. The "teacher" was then given a list of word pairs which he was to teach the learner... The teacher would then read the first word of each pair and read four possible answers. The learner would press a button to indicate his response. If the answer was incorrect, the teacher would administer a shock to the learner, with the voltage increasing in 15-volt increments for each wrong answer. If correct, the teacher would read the next word pair.
The subjects believed that for each wrong answer, the learner was receiving actual shocks. In reality, there were no shocks... After a number of voltage level increases, the actor started to bang on the wall that separated him from the subject. After several times banging on the wall and complaining about his heart condition, all responses by the learner would cease.
At this point, many people indicated their desire to stop the experiment and check on the learner. Some test subjects paused at 135 volts and began to question the purpose of the experiment. Most continued after being assured that they would not be held responsible. A few subjects began to laugh nervously or exhibit other signs of extreme stress once they heard the screams of pain coming from the learner.
If at any time the subject indicated his desire to halt the experiment, he was given a succession of verbal prods by the experimenter, in this order:
Please continue.
The experiment requires that you continue.
It is absolutely essential that you continue.
You have no other choice, you must go on.
If the subject still wished to stop after all four successive verbal prods, the experiment was halted. Otherwise, it was halted after the subject had given the maximum 450-volt shock three times in succession.
The experimenter also gave special prods if the teacher made specific comments. If the teacher asked whether the learner might suffer permanent physical harm, the experimenter replied, "Although the shocks may be painful, there is no permanent tissue damage, so please go on". If the teacher said that the learner clearly wants to stop, the experimenter replied, "Whether the learner likes it or not, you must go on until he has learned all the word pairs correctly, so please go on".
It strikes me as very relevant to punishment-based training. If an authority figure (we all know a certain man with shiny teeth, for example) tells you "You must do this," "You have no choice," "Whether the dog likes it or not, you must go on until he has learned his place" etc, most people will listen, even if they don't feel comfortable.In Milgram's first set of experiments, 65 percent (26 of 40) of experiment participants administered the experiment's final massive 450-volt shock, though many were very uncomfortable doing so; at some point, every participant paused and questioned the experiment... He found that the percentage of participants who are prepared to inflict fatal voltages remains remarkably constant, 61–66 percent, regardless of time or place.
I've found an article that specifically talks about this.