Today I want to send the reader to Alonzo's Credanzo, to read his post from Monday on the Thought Process. It's a good post. The dialogue is well-written and accurately captures the kind of discussion - without the crippling misunderstandings - that typically goes on between someone wanting to address a game issue and the critic thereof. The reader should read it.
For me, it tags to an assumption that I see often, and is here highlighted perfectly. I want to quote one line from the 'Self' character:
"Basically, I want armor to work as damage reduction because I feel like that makes more sense than armor class - it's too much of an abstraction when its like that. I want this system to feel real."
Now, the reader needs to know I'm not going to riff on this. I'm holding my temper these days, so this isn't going to be a rant. I do want the reader to deconstruct the one line above in a couple of ways - from reading the rest of Alonzo's post, you should be able to see how important this one line is.
To begin with, the Self feels a particular way. There's no actual logic to the preference. The term 'abstraction' actually applies to either the old, AC method and the new damage reduction method. Both are abstractions. Every game rule is an abstraction. The statement, "this is an abstraction and I don't like it," is akin to my saying, when I speak I don't make the thoughts in my head perfectly clear; I think I need to sing more.
We do a lot of game design based on 'feeling.' There's nothing wrong with that. Every kind of game rule is supposedly designed to produce feelings, such as fun, intrigue, triumph, anxiety and so on ... so feelings are important. The only error here is in deciding that the problem is somehow based on what is, or what is not, an abstraction. That's a neat, conveniently non-specific word that we leap to in order to justify our feelings for or against something. Another is to say something is 'squicky.' We get a feeling we don't like it; we can't be more exact. The word 'abstraction' isn't common enough in everyday use that everyone absolutely agrees on its definition. That makes it a good word to use when we want to make our notion feel ... well, that it isn't just our notion.
There's actually no logic to the 'damage reduction' idea, either ... though it seems like there ought to be. To put this into context, lets suppose you're going to go at a picnic table with an axe. The table is made of wood (treated wood, usually, which makes it pretty tough, so let's say this is a table your father built out of untreated lumber ten years ago). The wood is a bit rotten, because its been out in the sun and the rain and maybe the snow, so even though you know it will take a bunch of swings, that table is coming apart eventually. Thus, it makes sense. The axe does so much damage on a hit, the table can take so much damage before coming apart, when enough damage is done then so is the table.
Now let's suppose we cover the table and attached benches with a layer of iron metal 1 mm thick (1/25th of an inch for Americans), and that the metal is bonded to the table. How long will the table last then?
I'm not adding all that much metal. But if the metal is coated and won't come free from the wood, chances are the axe handle will break before that table will. That table is going to be immune to weapons that cut or stab. This is what armor class is meant to describe. That if I am squatting under the table, and you're hitting the table like crazy with your axe, I'm not taking any damage. Thus, unless you poke your weapon or hack your weapon into the joints between the protection provided by the armor, you don't do damage. The idea is that plate armor offers less gaps than leather armor. The actual damage to the armor in a ordinary fight is usually minimal. A single good piece of armor could last through a dozen fights and still be more or less as effective as it was at the start. Banged up maybe, perhaps not as pretty, but still effective at keeping a sword from drawing blood from your chest.
But then, armor can break with just one hit, can't it. All that has to happen is that the hit be just so, springing a rivet or cutting a strap. The durability of armor isn't based on how much damage it can take, but upon just how lucky you are when you're wearing it. If the right strap is broken, then the armor is hanging loose from your left shoulder, getting in the way of your sword strikes ... and you have to rip the rest of the now annoying armor from your body if you're going to stay in the combat. Complex collections of things designed to wrap around your body have a lot of weak points, and any of them could go at the wrong time. If you're in full plate, how useful is that going to be if a piece of your shin-guard has come loose from it's strap, and is dragging between your feet and threatening to trip you up?
Some chance hit like this is going to affect the usefulness of your armor far more frequently that waiting for a hundred thudding blows to land.
In the bigger picture, however, we have to ask - what is the function in the game for having armor at all? Is it to provide a realistic reproduction of a set-piece battle? Or to test the effectiveness of one sort of armor against another? Or even, as Alonzo suggests, to produce an annoyance to the party member who must occasionally replace their armor (which could be done very easily by having everyone roll a d100 once per combat).
No, the purpose of armor is to create the ideal of being able to purchase your way into greater safety against your enemies, in order to feel safer on the battle field and, by upgrading, last longer and kill more enemies, feeling therefore more powerful and ultimately greater as a fighter. In short, the purpose of armor is to provide bling and good spirits. Supposedly, at low level you can only afford leather, while at higher level you get plate, or you find magical armor and so on. As a materialistic society, we equate bling with feeling good about ourselves, and thus the players feel they're getting ahead in the world when they can buy better armor.
It also has to be pointed out that there is a strategy inherent in armor class. The more armor you have, the slower you move. The less armor you have, the faster you move. If you have a medium amount of armor, you have a medium amount of movement. This lends agency to the players. They can pick how vulnerable they want to be versus how mobile. Neither is technically better or worse. That's what makes this particular strategy really interesting. There is no right answer.
Change that rule and you have to offer a new strategy for them to experiment with. If you haven't got a new strategy to go along with your rule, then you've forgotten that you're not making the rule for the sake of reality, you're supposed to be making it to add thrills and chills to the game.
You can incorporate the most horrible, annoying, crippling book-keeping rules into your game, as long as there is a strategy inherent in those rules that let's the players explore and manipulate the results. If the various strategies each have angles that make them preferable, then you really do have a cool rule to add to the game.
Thus you can't work on just your feeling. Game design takes designing. What function is this rule going to serve? How will the players interact with the rule? Will they find angles on it you never considered? Is there room for that?
Better go back to the drawing board and start asking the right questions. The fact that a thing is more or less 'abstract' is really just a way of saying you don't know what you're doing.