That's the premise of armor making you harder to hit. Which is also pretty weak, of course, but a whole 'nuther sub-topic among the many deficiencies of D&D decried over the decades and done better by other games since the late 70s.
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OTHO, the premise of hps making you harder to kill is that whether a "hit" actually so much as touches you or musses your hair - or scratches you, or impales you fatally - is all dependent on the damage roll relative to your hps (and maybe even a poison save).
I guess my ideal would be the hit points as injury trip points, using hit locations, combined with armor as DR and weapons possibly having a penetration value that either offsets the DR or acts as a multiplier to damage. Every hit
is a hit - armor makes some of them glancing blows or cushions the impact or prevents penetration (which is historically why there was an armor vs weapon arms race). It makes helmets useful again. It eliminates the hand-waving of hit points as not really physical damage and the hand-waving of whether or not an attack roll that is successful is a culmination of a bunch of hits of which only one is significant enough to cause damage.
It makes no sense whatsoever that hp can somehow represent a combination of meat, luck, karma, etc. since poisons, environmental damage and energy attacks all currently subtract your hp the same as weapons. Suffocation drops you right to 0 hp, for example. That is totally at odds with poisons that subtract hp or weapons that subtract hp. The suffocation rules in my mind work the way you'd expect - you are instantly incapacitated after you've run out of air and lapse into unconsciousness.
If like to also see about applying the 3ed supplement on poisons that took a real world approach.
Burns, acid, freezing - they ought to have effects you'd expect rather than "the dragon breathes on you, take 60 damage or 30 if you save."
Dragons, giants, a pack of wolves, or a horde of ghouls ought to be a terrifying encounter for low level parties and still be a challenge for high level parties.
The ease of restoring your health through short and long rests after dropping to 0hp quickly becomes boring.
I want mechanics that support things like a PC getting separated during combat, getting knocked senseless and subsequently being drug off screaming by a ghoul dragging him back to his den to eat
while the combat is still ongoing. Those same mechanics also need to support a party working together to gang up on an unwary giant, or a fight where either side runs away instead of fighting to the death more often. A goblin raiding party or a hungry tiger ought to run away after taking a few good hits and deciding there are easier pickings elsewhere.