Obviously we’re all grateful to Mr. Petrov for not hitting that button, but it raises two points (for me at least):
1) It shows how careful you have to be when relying on a computer/automated system for critical tasks (and it also suggests that manual overrides right up until the last minute would be useful, as would self-destruct devices for ICBMs).
2) It shows that you can’t trust humans in that role. His computer system is telling him that the US has just started a nuclear attack on his country and he didn’t retaliate, not because he knew something was wrong, simply because he had a gut instinct that said it wasn’t. I’d like my country’s defence to be based on more than what one man feels. This is something that has been corroborated by tests on US personnel by instigating fake attacks and telling them to hit Launch (which wouldn’t have done anything anyway) only to find they’d refuse. It makes a complete shambles of the whole system.