Assign the role and the behavior follows.
Two studies, and they sit at opposite ends of the same mechanism.
Zimbardo's Stanford prison study in August 1971 assigned students to be guards or prisoners, and was terminated after six days when guard behavior escalated to sustained humiliation and abuse. Its standard interpretation — that ordinary people become cruel when a situation supplies the role — has been substantially challenged since. Archival work by Thibault Le Texier and by Alex Haslam and Stephen Reicher shows that guards were briefed on the behavior expected of them, that Zimbardo and his staff intervened to encourage toughness, and that the study lacked the controls its conclusions require. What it demonstrates is closer to the effect of an authority telling people what their role requires than the spontaneous emergence of cruelty.
That correction does not weaken this law. It sharpens it: the role must be communicated, and communicating it is the technique.
Rosenthal and Jacobson's Pygmalion in the Classroom is the softer and better-replicated half. Teachers were told, falsely, that certain randomly selected pupils were expected to bloom academically. Those pupils showed measurable gains. The teachers had not been given anything but a label, and the label changed how they taught — more attention, more warmth, more challenging material, more feedback — which changed the pupils' performance, which confirmed the label.
That is Merton's self-fulfilling prophecy with the causal chain visible.
The operational instruction is that naming somebody is a way of issuing an order without issuing one. Call a person reliable and they will work not to be the exception. Call a team elite and they will bear costs an ordinary team would refuse. Call someone difficult, in front of others, and their subsequent behavior will be read through it and will eventually conform to it.
The boundary is where the assigned role licenses conduct the person would otherwise refuse, and Zimbardo's own case is the illustration whichever interpretation you accept. A role supplied with permission — you are the enforcer here, this is what the job requires — is an instruction with the responsibility already displaced, which is chapter 279's agentic state arriving through a job title.
The negative version is equally consequential and considerably more common: a label applied to a child, a subordinate or a patient that organizes everyone's subsequent interpretation of them.
The counter is to reject the assignment explicitly, out loud, early.
Countered by The Recruiter’s Tells