xaxers said in comments here this:
AH! Let me explain to you what HP really represent, rather than just how many hits from a sword you can take:
Really, they're about how well you can avoid critical damage. The fighter with 200 hp? Look, that d8 damage from a sword isn't about him just being so tough and manly that he just ignores the stab wound, it's that he's so tough, manly, and good at not getting stabbed in the face that he moves out of the way of most of the blow, so that you just cut him a little bit. A peasant who has never held a sword? Yeah, you're going to stick him real good, right in his liver. Dead and gone, real quick like.
That is what having a high HP count does--you, without need for additional rolling, basically avoid most of the blow that otherwise did connect with your armor. You get a bruise or scrape instead of a broken skull or pierced lung because you moved at the last instant, or gave with the blow and reduced the impact, or whatever. The point is, your skill at combat is what saved your life from that blow.
In my opinion that explanation is one of the best for HP I've read this far. What do you think?