It happens in a car park, or across a street, or through a window. Someone raises a hand. You raise yours back. A fraction of a second later, their attention has moved past you to the person standing directly behind your left shoulder, the person they were actually greeting, the person whose existence you had not registered until this moment.
You are now standing with your hand partly raised, in mid-wave, waving at no one in particular, in full view of both the person who was not waving at you and the person they were waving at. You bring your hand down slowly. Everyone moves on. You will be thinking about this at 2am for the next four years.
The initial wave is not a mistake, exactly. It is the output of a very fast social recognition system that has been finely calibrated over millions of years of humans needing to identify whether nearby humans are friendly. A raised hand at close range, aimed in your direction, is a greeting. The most efficient response to a greeting is to return it. Your brain made that call before you were involved in the decision.
The problem is that the system is not designed for the specific social density of modern life, where people who know each other are distributed unpredictably throughout environments also populated by strangers. In a small village, anyone raising a hand in your direction was probably waving at you, because there were few enough people that the probability was high. In a car park, the probability is considerably lower, but the system does not update its priors with anything like the necessary speed.
What is interesting is the aftermath. The social error itself is brief. What lingers is the embarrassment, which is disproportionate to any actual harm done. Nobody is injured. Nothing is broken. At worst, two people witnessed you briefly wave at no one. And yet the feeling sits in the body as if something significant has occurred.
The reason for that is almost certainly that social errors have historically carried much higher stakes than they do now. Getting the signals wrong, misreading who was greeting whom, could cost you something in small close communities. The embarrassment response is the trace of that cost, still present long after the stakes have dropped to approximately nothing.
The wave was fine. It is the survival instinct dressed in civilian clothes, briefly confused.
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