The three-page paper that broke the definition of knowledge

For centuries, philosophers treated knowledge as simply a justified true belief. In 1963, Edmund Gettier published a short paper with two scenarios where someone holds a justified true belief that still doesn't feel like knowledge, because it turns out true only by luck. The paper reshaped epistemology, spawning decades of attempts to patch the definition with a missing fourth condition.

— Edmund L. Gettier, Is Justified True Belief Knowledge? — Analysis, Vol. 23, No. 6, June 1963