Imagine if you were a guard in an evil villain's fortress, which is being infiltrated by James Bond. You are going to appear on screen for about one second in your black turtle neck uniform. And to get past you, he's going to have to kill you. The 25 years of your life are going to go to nothing - your parent's love, your schooling experience, military training, plans for the future, all gone, just so he could go through one hall undetected (and probably get caught and held captive later, anyway).
Don't you wish you could just make a deal with him? You know he could kill you, there's no point in wasting your life to prove that. But he has to kill you, because if he lets you go, you might raise the alarm. Wouldn't it be great if you could just forgo the killing part? The problem is, he can't trust that you won't just lie, and you would be worried about what would happen to you later, if Bond was captured and your boss asked why you hadn't stopped him. Even if you make a deal with him to not reveal your betrayal, he might sell you out later anyway.
So it's a problem of trust between you - he needs to be able to trust you, and you need to have an explanation for what happened that he won't undercut.
But how can you build this trust? A history-based system would be so fragile - it'd require a huge reputation tracking system (AKA honor) and would still be broken all the time.
But a physical system, in a pre-genetic-engineering time, is so powerful. If it was known that people simply had these vulnerabilities, and they always worked, it would be undeniable - everyone would be vulnerable.
Sort of like the vulcan death grip, or the vulnerability to "mickeys" - we want these vulnerabilities so that people who totally have the drop on us don't have to kill us. If we are outclassed and have lost already, we want to be able to prove we are "knocked out" and out of the game for a while, without having to be killed.
So, what if humans had a vulnerable place, which would be guaranteed to knock us out for an hour if tapped. Along with that, what about a memory-knockout - a spot on our head that if you push, it would make you forget everything in the last hour.
So many murders would be avoided if this existed - a physical way to pass someone, or make someone forget something. If it was just a deal or a promise on both sides part, it could be broken - but a built-in, human characteristic like this would be great!
But, we don't have it - and even if we engineered it later, the person confronting you would not be able to be sure you didn't just fake the thing, and will rise up 2 minutes later and shoot them in the back. It only works in a world where there is clearly no genetic engineering going on.
If Goons unionized, they could institute something like "tapping out" - perhaps a uniform with a red spot on the back. If Bond touches the spot, you would just be bound to not raise the alarm and pretend he killed you. Otherwise, everything would be the same (you could still fight if he doesn't manage to achieve it). But this would not work that well - a physical solution would be much better:
Your union would issue you with an actual "knockout-button" that you would wear on the back of your neck. It'd be a little red button, and if Bond pushed it, you would be knocked out for an hour, guaranteed. It would be against union rules to obscure it. Even though this would be a weakness, it would actually be good for you to have this - it'd save you getting killed all the time. Since Bond is never stopped by minor villains anyway, it would not make it particularly easier for him to get into the fortress.
Of course, the evil villain would try to stop you from wearing this - but that's what the union would be for, to require the villain to only employ red-buttoned insta-knockout enabled goons.