Wrong. A knockout is the result of someone's brain suddenly getting rattled inside the skull/hitting against the skull.
And to the people saying that skull thickness plays a factor. Wrong. The skull is a bone. It encases the brain. I just told you that a knockout is a result of the chin (the "fulcrum" of the head "machine") being struck with such velocity that it causes the head to suddenly jerk, which makes the brain rattle for a second. How does thickness lay into that?
And I'm really surprised that people thought the "chin" was literally the knockout button. You can't be that dumb? It just so happens that the chin is the the perfect "balance" spot (fulcrum) where it's the center section where hitting it disturbs the balance. i worded that fucked up, and probably didn't even use the word fulcrum correctly. What I'm getting at is, if you were to look at a big giant ball, let's a say a bowling ball, resting on a relatively small point, and your task is to knock that shit off balance, where do you think you'll have best sucess? Graze the top of the bowling ball? Hit it head on in the middle? Or hit the shit out of the "fulcrum" , the weak point where the balance is distributed?
The chin.
So after talking a bunch of nonsense, my long winded answer is no. Skull thickness has ZERO to do with it. I'm not prepared to argue neck muscles though. I can't get past the logical barrier about how a punch can be weakened by "rolling with it," e.g. turning your head in the same direction that the punch is moving, boxers are great at this. So, they are slowing down the momentum of the punch, in other words elongating the impact time (this is a simple concept; think about why it doesn't hurt as much when you jump off a high point and bend your knees as you land. You lengthened the impact time, taking off momentum). SO.......having thick neck muscles.....that DOESN'T roll with the punch....in fact, you could argue the neck muscles will absorb the impact and DEFINITELY wouldn't lengthen the moment of impact. So I don't see how that could protect against KOs. It seems it would happen more frequently since you're no longer rolling with the punch, but in fact completely absorbing and eating it. But anecdotal evidence seems to go against everything I just said so I won't defend this point too much. There must be other variables I'm completely overlooking.