Roger Bannister

British middle-distance runner and neurologist who on May 6, 1954 became the first person to run a mile in under 4 minutes — a feat many had deemed physiologically impossible — and whose achievement was replicated by dozens of runners within the following year.

Provides the canonical example that psychological belief is a real physiological constraint — the 4-minute mile was broken not because human physiology suddenly changed but because his achievement demonstrated it was possible, and within a year dozens of runners crossed the barrier — making belief in possibility a genuine performance variable.