On a night in September 1983, the Soviet early warning system told Petrov that the United States had launched missiles. Then it said five. Protocol was to report it up the chain, where a retaliation decision would be made in minutes.
He didn't. It felt wrong to him: a real first strike would be hundreds of missiles, not five, and the system was new. He reported a malfunction. He was right; sunlight on high clouds had fooled the satellites.
He wasn't rewarded. He was reprimanded for paperwork and quietly moved aside. Most people only heard about it years later.