|The infamous "Enigma of Greyhawk" is, I think, a metaphor
for all of OD&D. Because this game is batshit.
See, it all starts when I'm talking to one of my players about edition history. "Before 3rd Edition, D&D didn't have a unified task resolution system." What? How? You mean the core mechanic? Yeah, I mean there was no core mechanic. No "d20 + modifier against DC". So how did you do stuff? Two main ways: either you just talk it out and describe it in words and resolve it that way, or there's some weird ad-hoc task resolution system. So for finding and disabling a trap, the DM just has to visually describe the trap and the player has to describe what they do to it. But then, maybe for something like climbing a cliffside, you roll d%, where your percentage chance of success is derived from a lot of weird variables and there's a table you consult that tells you the answer. Lots of tasks needed some variation of d%, or roll a d6, or consult a matrix, or maybe roll a d20 but, like, I dunno, roll under maybe? And abilities were almost never a part of this.
So they ask me, "were abilities created in 3rd edition then?" Nope. So what were they for?? Well, two things. First, think of all the miscellaneous secondary purposes of a lot of abilities. Charisma is how many henchmen followers you can command. Constitution determines health and healing. Intelligence and Wisdom help Magic-Users and Clerics prepare spells, or something. Dexterity is added to ranged attacks, AC, and initiative. Strength is added to melee attacks and is used when opening stuck doors. Yes, because apparently stuck doors were that common that it was one of the only purposes for your Strength attribute.
But the second thing is bigger. I've even heard some OD&D fans claim that they think it's the only thing abilities should have ever been used for. And that's gunna sound pretty fuckin' zany at first. Abilities factor into the rate at which you gain experience points (XP). As in, every class had a "Prime Requisite" ability that mattered for it (e.g. Strength for Fighting-Men, Intelligence for Magic-Users, Wisdom for Clerics). If the score of your prime requisite ability was really high or really low, then you gain XP faster or slower. They can be a prerequisite for multi-classing (switching class? Maybe it's different from multi-classing) and for some classes, such as the Paladin. But basically, the main thing that good abilities do is help you level up faster. And this is the same edition that made you roll all your abilities randomly, in order.
So my player is, at this point, pretty thoroughly flabbergasted. If you're an old-school gamer, it's probably all familiar to you, so you just think, "yeah, that's the way it was back in the day." And you probably think that either 1) they've since "fixed" it, or 2) it was basically fine and you just learn how to play the game as it is. But to my young player? This sounds awful. This just sounds punishing and unfair to people who rolled poorly, because their friend who rolled high is also going to be out-leveling everyone in the party. Why would you even bother playing a shitty character if you can't even look forward to them improving much?
Well, what if I told you that you won't just be playing one character?
It used to be the norm that everyone had a good handful of characters, and quite a few henchmen. Now, you could play as many of them at once, but from what I've read it's still the case that you generally only controlled one at a time. But the others were back home waiting. After all, it might take your Magic-User a couple weeks to recuperate from their injuries, so in the meantime you should play your Fighting-Man. So you have a collection of people who you are working on, like your own personal party of adventurers. Also, 1-on-1 adventuring between the DM and 1 player was way more common back then, so it wasn't unreasonable to take one or two of your weak PCs out for a dungeon-run on their own to grind for XP, so they can catch up to the others.
If you don't already know all of this, then I strongly recommend you read this free Patreon post that covers it well from a modern perspective. The first evidence I dug up on it was from here and here (the words of Tim Kask!). They focus a bit more on the principle of the "open table" campaign, which is definitely interesting and valuable and something that needs more attention. But I want to go a bit more in depth on the "stable of characters" concept itself.
See, I once heard someone say (and unfortunately, I cannot, for the life of me, find a source for this) that it all makes sense when you realize that XP is shared among your characters. You know how Magic-Users kinda suck at level 1 but have the potential to be the most powerful of all? How about you skip their low-level grinding by sending in some meatshields to go gather XP for them and bring it home. In a way, it's more like you're building a strong team, like X-COM. You regularly get new, randomly-generated bozos who may be shitty, average, or spectacular. You have to figure out how to optimize the best team composition with what you've been given, and it's gunna involve a lot of long-term "campaign play" investment. And the fact that there are super-classes like the Paladin that are only playable by people who were lucky enough to roll God stats doesn't seem so broken when you realize that, like, there's probably just going to be one or maybe two Paladins in the entire greater party of you and all your friends. If someone was lucky enough to get that, everyone else is gunna say "GO FOR IT! DON'T WASTE THIS! We have a chance to roll with an actual Paladin!"
Okay, but how is XP shared? That doesn't make sense. How does the Magic-User's adventure benefit the Cleric back home? Again, it makes sense when you remember that most XP is earned from gold and treasure. You have to pay to level up. And gold is easy enough to pass hands between your characters. Your peons bring home the bacon for the big guys. But still, how does gold turn into greater power?? That, I'll admit, wouldn't be justifiable in most editions. But just pay attention to the things you get in OD&D specifically. What are the benefits of leveling up? Mostly stuff that you could hypothetically pay for. I think a Fighting-Man might get an increase to their attack bonus, so maybe that'll have to be justified as payment towards "training" or something. But the real meat and potatoes are 1) strongholds and baronies and armies and whatnot for Fighting-Men, 2) new spells for the Magic-User (whose to say that maybe those are only unlocked by paying for them? Buy the books and ink and experiment materials and do the research and whatnot), and 3) new spells for the Cleric (alright, we know their spells are bestowed by their god. But maybe they receive more because they're donating so much to the church/charity. Maybe Clerics put their treasure toward an ongoing Cathedral construction fund or something, and that's why they keep getting new miracles.)
Isn't this cool? Like, doesn't this sound like a fascinating way to play? It makes randomly-generated characters seem a lot more sensible, and it forces you to really invest in a lot of downtime and focus on the long-term prosperity of your characters. Their place in the world, not just in the current adventure-of-the-week.
But also, you might notice some gaps. For example, how many characters go into a stable? Without a hard limit, what's to stop a player from making more and more and more random characters until they get a handful of Paladins? How can you always justify a connection between each of your characters? What if you just have one character, or at least one type of character, who you always want to play as? There are plenty of issues, and the DM would just have to decide on some guidelines. But I also don't even feel like you need to commit to the whole vision to get something out of this.
Like, I don't use Gold-for-XP in my game. I have my own weird leveling system now. But I do want to include the Stable-of-Characters format. It won't be so much about grinding XP for each other and building your perfect X-COM team or whatever. But it will force players to juggle between a handful of characters while their other guy is busy with downtime stuff, like running a business, doing research, recuperating from injuries, etc. This is the main reason I require at least a week off from adventuring in order to level up in my own system, BRAVE. And because my game is pretty lethal, I don't want it to be too painful for you to keep losing characters. You always have a couple that you've been making steady progress on, and as long as you're careful in how you deploy them, you can gradually get one of them to a respectable status.
However, I think someone else should explore the Gold-for-XP-but-we-can-trade-that-gold direction further and do something interesting with it. Build a whole game around it, because it's fucking cool. My favorite "take" of the OSR is the emphasis on the "Renaissance" part. Not playing old editions and their retroclones, but instead playing new games that iterate further on old, abandoned ideas. This is one of the coolest ones I know of, too.