How did Stanislav Petrov save the world?

On 26 September 1983, Stanislav Petrov, a lieutenant colonel in the Soviet Air Defence Forces, was on duty at the Serpukhov-15 bunker, monitoring the Soviet early warning satellite system, Oko. When the computers detected an incoming missile from the United States, Petrov suspected a false alarm due to the unlikely scenario of a single missile launch. Despite protocol dictating immediate nuclear retaliation, Petrov's training and intuition led him to dismiss the warning as erroneous. The subsequent detection of multiple missiles only reinforced his scepticism. Ultimately, Petrov's decision prevented an unnecessary escalation, later attributed to a rare atmospheric phenomenon and satellite misalignment.

https://en.wikipedia.org/wiki/1983_Soviet_nuclear_false_alarm_incident

https://en.wikipedia.org/wiki/Stanislav_Petrov