It shows that people consistently underestimate the physical forces they apply as opposed to the ones applied to them, or, in the researchers' words "self-generated forces are perceived as weaker than externally generated forces of the same magnitude, which arises from a predictive process in which the sensory consequences of the movement are anticipated and partially removed from the perception".
Predictive Processing theory explains this finding and others (such as people not generally being able to tickle themselves) by proposing that the brain cancels out stimuli it can predict.
I think a general version of this may be at work here. People underestimating the impact of their own actions and strongly feel the impact of others' actions. They can each truthfully say "from my own frame of reference I was perfectly stationary when that guy crashed into me".
Regarding where underdog bias comes from, I think this study may hold a clue
https://paulbays.com/pdf/SheBayFri03.pdf
It shows that people consistently underestimate the physical forces they apply as opposed to the ones applied to them, or, in the researchers' words "self-generated forces are perceived as weaker than externally generated forces of the same magnitude, which arises from a predictive process in which the sensory consequences of the movement are anticipated and partially removed from the perception".
Predictive Processing theory explains this finding and others (such as people not generally being able to tickle themselves) by proposing that the brain cancels out stimuli it can predict.
I think a general version of this may be at work here. People underestimating the impact of their own actions and strongly feel the impact of others' actions. They can each truthfully say "from my own frame of reference I was perfectly stationary when that guy crashed into me".