Placebo Effect
The phenomenon where a patient is given a decoy intervention (sugar pill, fake surgery, etc. — the 'placebo'), where they believe they are receiving a 'real' intervention, and they in fact demonstrate measurable positive clinical outcomes.
Origin
Placebo is Latin for "I shall please" — a phrase that by the 16th century had acquired a derogatory sense of empty flattery. Scottish physician William Cullen applied it to medicine in 1772, describing a treatment given "more to please than to benefit the patient." The measurable physiological reality of the effect — beyond mere suggestion — was established as randomized controlled trials became widespread in the 1940s, and formalized by Henry Beecher's 1955 paper "The Powerful Placebo," which documented consistent positive outcomes across 15 controlled studies of inert treatments.