The Soviet leadership was frightened, and had a view of Reagan not unlike that of the US government about Kim Jong-un today.
They feared a surprise attack designed to destroy all their nuclear missiles and bombers on the ground, and so had moved to "launch on warning" mode. If Colonel Petrov reported what his screen was telling him, the machinery of Armageddon could start moving very quickly.
Stanislav Petrov didn't report it. It was a new system, and it could be making a mistake.
Besides, he knew that you only get one chance at a surprise attack, so logic says you should launch all your missiles at once - more than a thousand of them, in the case of the US. Launching just five would be beyond stupid. So he waited.
And waited, for 23 eternal minutes, to see if the Soviet Union's ground radars also picked up the incoming missiles as they descended towards their targets. They didn't. "I realised that nothing had happened. If there had been a real strike, then I would already know about it. It was such a relief."
He was an ordinary man who did one extraordinary thing in his life, but think of the courage it took to ignore his orders, trust his judgment, and risk exposing his country to a surprise nuclear attack. Think of what went through his mind in those 23 minutes. He was a hero.
No good deed goes unpunished, so Petrov was reprimanded for failing to describe the incident in his logbook.
He was initially praised by his commanding officer for doing the right thing, but then it was realised that if he was rewarded, the senior people responsible for the system that produced the error would be punished. So he was sidelined, retired early, and later had a nervous breakdown.
And the system error? The satellite had spotted a rare alignment of sunlight, reflected from the cloud-tops over the US Minuteman fields, that resembled missile launch tracks to its simple-minded image-reading device.
There were similar incidents during the Cold War - a US over-the-horizon radar once reported Moonrise as a mass missile launch - but this was the only one that happened when the relevant side was in launch-on-warning mode.
Given how full of bugs the missile-detection programmes were, it's remarkable that the US and the Soviets got through 40 years of the Cold War unharmed. Full credit to the professionals on both sides who understood how grave the consequences would be if they got it wrong, and relied on their own intelligence and experience when confronted with terrifying data from machines.
Full credit, too, to the leaders who stayed calm and never actually threatened each other. Occasionally they declared the other side doomed by history - Nikita Khrushchev's famous "we will bury you" comment in 1956, Reagan's "write the final pages of (Soviet) history" speech of 1983 - but they were always talking about the other side's economic and political defeat, not its nuclear annihilation.
Things are different now. Kim Jong-un's lunatic threat to "sink" Japan and reduce the US to "ashes and darkness" with his handful of nuclear weapons, like Donald Trump's all-too credible threat to "totally destroy North Korea" (that's 25 million people barbecued, irradiated or simply vapourised, if he means what he says), go far beyond the language that was used during the Cold War.
It would be reassuring to know the professional military on both sides, at least, are as responsible now as they were then. Alas, we don't know that.
¦Gwynne Dyer is an independent journalist published in 45 countries.
