The Mule Problem

The Mule — a mutant who can manipulate emotions directly — derails the Seldon Plan entirely. He represents the unpredictable individual that statistical models cannot account for: the black swan, the unprecedented event, the person who changes everything.

The tension between historical inevitability and individual agency drives the entire series. If psychohistory works, free will is an illusion. If individuals can derail the Plan, psychohistory is unreliable. Asimov never lets either side win.