Hit points (HP) abstract into a single number how much more a character can endure: they drop with each injury, and at zero the character falls or dies. They are a game convention lumping together the depth of wounds, stamina, luck, and will, and the "health bar" of countless video games branched from here.
Reducing a life to one number and counting it down stands in the same place as our world’s ledger, which writes a person’s worth as a figure and subtracts from it.