Okay, sure, maybe I'm wrong on animals. I don't fight animals in real life much.
Part of the difficulty is that the D&D hit points abstraction makes things very different from real life, or even TV/movie combat. A D&D adversary with one hit point is as deadly a threat as an un-injured one. A real-life human beaten so badly they drop? Even if they're not dead, you probably have a few minutes to turn your attention to the others swinging swords and throwing magic at you.
