Ever heard of situational awareness?
Wifey and I like to go for a fast walk in our town along a busy street that has a wide sidewalk. At every street light post (about 30 paces) I look behind us to see if anyone is approaching from the rear. (My version of a Crazy Ivan!)
Several times, we've been behind other people and they NEVER look behind them. If we're walking faster than they are and we pass them, they have no idea anyone was behind them at all.
Yes. But other than having eyes in the back of your head, this doesn’t apply to the typical knockout. The case at hand in atypical in that the victims were aware they were being followed.