The Bay of Pigs

Kennedy's inner circle unanimously approved the 1961 invasion plan even though, on any cool review, it was badly flawed. Several advisors later admitted they had serious doubts at the time but stayed quiet because everyone else seemed confident.

When the invasion failed, Kennedy rebuilt his advisory process to stop it happening again. He began leaving the room during early discussion, assigned formal devil's advocates, and made dissent a job duty rather than a social risk. The Cuban Missile Crisis 18 months later was handled through those reformed processes, and a possible nuclear war was averted.