Sometimes, I like to experiment with obfuscation of the values, so players can 'roleplay' better, instead of:
Obfuscating the Hit Points
Back in version 1, 2 and even some of 3, I had the old hit points. Players would start with approx. 10, and gain approx. 1-2 per level. When they got wounded, they'd lose HP, when healed, gain HP, when at 0, start making unconscious checks, and at -3 death checks. very old-school.
Players could take extra bonuses in health, KO or death scores.. one player devoted his hero points to this, and at 18th level, had well over 75 HP, a KO of -7 and death at -7 more (-14). Based on the ruling at the time, it was near impossible to kill him. he soaked so much damage, could out last any opponent of similar level.
Players would have, the same above conversation, the tactical advantage of knowing how many HP they had, if they should heal a person or not, based on values, that in real life don't exist. I wanted to get that movie moment, when one character is 'dying' then later they pull it together and keep going, then when their adrenaline kicks in, they do some amazing stuff, even though they're "dying".
So I tried this out (You can use this for a game attempt, its kind fun, for GMs, but might be a little math intensive for younger GMs)
The Hurt System:
First, you make a quick note of players Health, Stress, and the CON and WLP bonuses or your games equivalent for health stats and mental health stats. Players can 'cope' with their Willpower bonuses of damage, but they can take Constitution worth of actual damage.
The point is, to not tell players how close to death they are, just tell them how close to death they FEEL. A player unhurt, will feel like the first cut is far worse than it is, based on how much pain they can normally cope with (their CON bonus), but once in pain, further hits don't feel as bad, because they are already in pain the distraction and adrenaline, will make them feel like the same amount of pain, is actually less.
The way to do this is to glance at the damage done, divide it by the willpower/pain bonus and tell the player "The blade cuts deep into your flesh, you are in extreme pain" according to how much the results were.
When a player is 'hurt' you inform them to write "hurt" in their health box, If they are in extreme pain, they write extreme pain.
0-1: Light grazing, 1-2: Hurt, 2-3 badly hurt/ cut deep 3-4: extremely wounded, 4-5 dangerously wounded, 5-6 mortally wounded, 6+ at deaths door.
But here's the rub, A player with 30 health, taking 10 damage, with a pain of 3, is going to be at stage 4 (round up) but another player, with 20 health, taking 4 damage, with a pain of 1 is going to be at pain stage 4 too.
So, then after the 1st wound, when a player takes a 2nd wound, you reduce the 'pain' by their con bonus, to account for adrenaline kicking in..
Player #1 with 30 health, takes another 10 damage, which would be 4 more pain, but her con reduces it by 2, so she only gets 2 more pain levels.. the pain from the wound is just badly wounded, but the total of 6 is mortally wounded, so you'd inform the player they were wounded, and they can feel the icy grip of death nearing.
Player #2, with 20 health, took another 4 damage, since their pain threshold is 1, they feel like they have taken a grievous wound, but since their con bonus is 2, and the total damage is only 8, they are only at the extremely wounded stage (4) rather than their pain threshold level of 8.
Player #1, with 2/3rd of their health gone, is feeling like death, their individual wounds don't feel so bad, but over all they feel bad. Player #2 takes each wound like they are deadly, yet overall are feeling ok.
The purpose here is not to be specific, but instead more descriptive, so the player can easily identify if they are going to die based, not on actual health, but on perceived health.
The Threshold System
Another, less mathmatical intense version is to just keep track of the most wounds they have ever taken, setting an 'invisible' 0, then dividing the difference into 4 or more 'stages'..
The above example, we reset, player #1 with 30 hit points.. takes 10 points of damage (a deadly blow, almost killing them!) in their first battle, so the GM jots down 10 as their threshold.
In the next battle, the player takes a quick 3 pt wound, the GM says its a major gash, as its above 1/4th of the threshold, another 5 point wound is also a major gash, later a 3rd major gash pushes their new maximum to 13, and the GM informs the player they are at deaths door as they've gone above their maximum from before.. They retreat from battle, 'barely surviving'
In the next battle, their next 3pt wound is not a major gash, since now, the 1/4th of 13 is 3.25, instead its a minor gash (from the players perspective) yet the 5pt wound is still a major gash.. the player, having seen the earlier 3pt and understood it to be a major gash, now, with another 3pt its a minor gash, wonders... hmm, ok, so I can take more damage than I thought, and like anyone in real life, is probably going to think, Oh, I'm tougher.. rather than 'hey I levelled up'
When they do level up, you increase their actual HP as per normal rules, but you only increase their pain threshold by 1 pt. This works well when you don't announce level ups too, players slowly get used to rolling more successes, but never know their own numbers, just general ideas.. but this is heavy load on the GM to track all players, and only the most pro GMs can handle this level of obfuscation.
My Current System
Players, not comfortable with not knowing their damage ratio to death, caused me to try this tactic, which seems to work best for now.
Health points act as the kind of 'threshold' above, if a player has 10 health, they can take 2.5 points of damage, without blinking, if they increase their 'pain' score with skills, it applies to this value.
Once they pass this threshold, the GM warns them, they are now able to be killed. players get cautious when they know any single blow can kill them. which is the effect desired.
Beyond this, players taking damage make system shock tests based on their will power and or constitution, determined by the damage taken vs the total damage already taken.
To evade the constant math that players can sometimes struggle with, the GM will inform them to write in the pain they've taken from any given blow, and the player can see for themselves, what kind of pain they are in. Pain causes negatives to the charactersheet, So players knowing they've taken 1 pain will usually start to question the cost benefit of pushing the battle vs the slippery slope of going on.
Conclusion
The key here, players, will never quite know how far they can push their health & wounds, only the GM, for sandbox games, the GM merely lets players learn via trial and error as to their actual health threshold, and for Narrative style games the GM can allow a wounded character to push on, past actual death, so they can complete the story, and players who have decided to ruin a game, can die off quickly and be asked to leave, without needing to justify the dice results.