Both true, and yet still it doesn't mean you have to fire the poor guy if the mistake was honest, regardless of damage done. Hell, he'll probably be beating himself over it harder than you imagine if the consequences were big.

Also, this: http://i.stack.imgur.com/eJy3b.jpg.

I disagree. Would an average user, the kind of person who is going to trust updates from Microsoft and leave them on by default and therefore wind up installing in this case in the first place, necessarily realise the significance of one extra confirmation dialog? People are notoriously blind to such messages, so I'd want to see exactly what that extra human intervention involved before making any judgement here.