Self-fulfilling prophecy
Etymology
Sociologist Robert K. Merton coined the term in a 1948 essay, building on the “Thomas theorem”: if people define situations as real, they are real in their consequences. His illustration was a rumor of insolvency that triggers a bank run and thereby causes the collapse it predicted.
noun phrase · /self-fool-FIL-ing PROF-uh-see/
A prediction that causes itself to come true because people act as if it were already so.
What it names
The loop in which believing an outcome — a bank failing, a student succeeding — produces the behavior that makes it real.
Example
Convinced the team would lose, players stopped trying — a self-fulfilling prophecy that guaranteed the defeat.
Related idea
A self-fulfilling prophecy makes a false belief come true through action; the Pygmalion effect is the specific case where others’ high expectations lift a person’s performance, and the placebo is its bodily cousin.