[I want to explain] the somewhat vague notion of "advantage" in combat. The superior side in any challenge can force the weaker side to exert themselves more and more to counter feints and blows designed specifically to stretch the weaker side's limits. A hit is generally only scored after your opponent's guard has been worn down - all the attacks prior to that are really preliminaries, not really made to hurt but to force the target to take more and more extreme defensive actions. I believe this is most easily observed in tennis - how the player who has the initiative (or advantage - no relation to DnD initiative) forces his opponents to run further and further with each ball, and finally sends the ball to the opposite side of the court from where his opponent is, making that ball impossible to catch. It is not any single ball that is impossible to catch, it is the sequence of balls that builds a pattern where the opponent is forced into an impossible situation.
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I do think that the above can be used as an explanation for hit points and why there is no physical damage until you reach zero hit points - any damage before that point simply represents building advantage. In my homebrew, I also use this assumption to motivate why hits below that threshold is recovered very quickly.
