This comes up from time to time on forums, blogs, in person, everywhere. It's one of the age-old D&D questions.
The common response is usually something like this -- Hit points are a mixture of luck, endurance, and combat skill.
- Luck? -- perhaps, but then, shouldn't halflings have a shit-ton?
- Endurance? -- that's certainly a part of it.
- Combat skill? -- this actually makes the most sense, according to the game's mechanics in the fact that martials get the most hit points. In this case it represents your ability to dodge, parry, and roll with it. As you gain levels, you get more hit points, meaning, you're becoming a better fighter. Kind of boring, but that should be the end of it.
It's the inconsistencies that keep this question alive.
If it is luck, endurance, combat skill, and not "meat points" then why do smaller creatures have fewer hit points than larger ones? Is an elephant a luckier, more skilled combatant than a badger? A troll has far more hit points than a pixie. Pixies might be small and hard to hit, but once you "hit" them, they're dead. Seems like meat points to me.
You could interject here and say, shut up and enjoy the game (or even better -- play GURPS) and you would not be wrong. Just keep reading...
Hit points work just fine as meat points... until you have, say 100, 150, 300, etc. Then things get harder to justify. On a side note, I find it fascinating that with every new edition of the game, hit point bloat gets worse and worse. 4th Edition was the worst offender (at just about everything) but 5th Edition only dialed it back a little. Can these people not design a fun game without everything having hundreds and hundreds of hit points? Still trying to emulate fantasy computer games that ironically started off trying to emulate you...
When people concern themselves with the vagueness of hit points, what they actually crave, I think, is a bit of realism (though I use the word "realism" perhaps "grit" is the better term, because ultimately, there's nothing realistic here.)
They want to see blood. The more vague combat gets, the less fun it is. Players want to know, "Did my sword actually hit the ogre this time, or do I only get to actually hit the ogre when it dies?" When that minotaur scored a critical hit with it's massive battle-axe, what in actuality, just happened to me? Did he simply swing so close to my head that it rattled my nerves for 18 points of damage?
For those that argue for the luck/parry/endurance explanation, is it really "realistic" to say that the only time you actually get hit in violent, medieval combat, is when you suffer the killing blow? Is that even fun? Then again, to be fair, that crowd is not aiming for realism or grit. Of course this is further convoluted by the fact that the length of the combat round varies over the editions from 6 seconds to 1 minute, and a lot of things can happen in 1 minute. But... that doesn't mean that at the end of that round, when you've taken a hit, that you haven't actually taken a "hit."
We've all exhausted this topic, yet the hobby will never be done with it. Simulationist vs gamist, sport vs war...
I've always been very descriptive with combat. I like a "hit" to be a "hit." Which is probably why I like opposed combat rolls and parry options.
If you've been "hit" by an arrow, then you've been HIT by an arrow! Sword & Sorcery fiction and imagery is packed full of heroes carrying on the fight with arrows sticking out of them. It's almost a trope. It's easy to explain too, because often arrows don't penetrate that deep or hit vital organs, and if you have any kind of armor on, it's even easier still, because it's mostly stuck in the armor.
The same can be said of weapon hits. Yes, you did actually just take a hit from that guy's battle-axe, but he didn't lop your head off, or your hand for that matter. You've been cut, you are bleeding... a bit, you are losing hit points and yes an elephant does have more hit points than you because it can physically survive more hits from that axe than you. But, you're tough, gritty, you're a pulp hero, you can take it! It's simply not necessary to say that you've been dodging and parrying and weaving in and out of blows, or you're just plain lucky. No! Your ass just got stabbed! Now fight on! This is the bread and butter of pulp fiction.
So... what happens when you fail your saving throw against something like a dragon's breath weapon? Mr. pulp hero just took the full brunt of 37 points of damage from a blast of fire and only has 3 hit points left. Those that made their save only took half damage, they merely got singed as they dove for cover. Not you...
What does that look like?
It should look like something "permanent" if you ask me. You have most certainly suffered serious burns. If the undead leave lasting effects from their touch, iconic attacks like dragon breath should do the same, and at the moment, I suggest 1 point lost from a random ability per 15 points of dragon breath damage taken on a failed save. There's a touch of grit for ya. You can even apply this principal to critical hits and level drain, but in those cases I would only make it 1 point lost in total and perhaps only after a failed death save.
So, you might level up and get better at what you do, but your body is taking a beating and showing the scars. That's a simple way to add some realism or "grit" to your game (and panic not, my friends, dungeons are full of ability-raising tricks!) Also, with realism in mind, "system-shock" rules should not be ignored.
As you gain levels, you do gain more damage resilience and the ability to avoid the killing blow. This is the endurance and combat savvy aspect of hit points. Regardless, when you've been hit, you are taking actual damage.
On a bit of a tangent, the size of dragons has also gotten out of control. They're iconic and they should be dangerous, but they're not Godzilla. If a lone, valorous knight is expected to have a chance...
Also, speaking of dragon breath, we all know the house rule, "Shields shall be splintered," well, they shall be "melted" too:
- Sacrifice your shield to turn a failed dragon breath save into a successful one, or half damage into no damage (doesn't work against poison gas.)
Clearly, your characters aren't going to lose limbs, but they will be cut and bitten and torn and burned... they will be scarred, and yet, the mythical underworld calls... again and again.
You're not playing village wimps.