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 fin... (read more)
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 fin... (read more)