If you are the average D&D player, you have been trained by structured play in two truths:
- D&D is there to tell your story
- D&D must have structured and balanced encounters
These assumptions will get your character, and quite likely the entire party, killed in old-school play.
The wandering monster table does not care about throwing multiple very hard encounters at you, the longer you stay in that hole in the ground. You could roll badly for wandering monsters three times in a row, get overwhelmed, and the entire party is killed in a span of an hour.
The "environmental simulation system" of old-school play and BX does not care one bit about "your story" or "encounter balance." The world is rigged against you. You are always meant to die. The thrill is figuring out how not to.
Wizards of the Coast loves the facade of balanced encounters and story adventures, since these make for better new-player experiences. Players should feel thrilled that they went through a dungeon, completed the story of the adventure, advanced their personal stories, saved the day, and, in the end, "everybody wins." You look at the structure of any modern adventure, and it is 90% this.
Kobold Press and EN World work by this 5E assumption, too; you will find balanced encounters and a focus on narrative play in those systems as well. You cannot escape this, and you assume it is the norm.
Old-school play?
To heck with that, you are being dropped straight in the middle of a world simulator, and there are chances based on the time spent and the location you are in to encounter monsters. While the map may be keyed with monster listings, the world isn't, and you must get in, get out, manage scarce resources, find safe places, and survive long enough to head back to civilization and find a moment to rest.
All the while, wandering dungeon monsters and wilderness encounters are being rolled for. If the number on the table results in a TPK encounter, so be it. You decided to take this risk, go a little further out this time, explore one more room, and you paid the price.
This is not about a preset story, yours or the adventure's. If you are lucky enough to live that long, maybe you can tell another part of yours. A story is something that comes out of your efforts to explore the world and survive the chaos, and personal stories are something on top of that.
If you were ever into game modding, this is like taking Skyrim and adding all these "random world encounters" and "kingdom battle" mods into the game that introduces random groups on NPCs and monsters onto the map, and you can stumble into the middle of a fight where wolves are fighting with a caravan of traders, and you can choose to jump in, ignore them, or just watch and loot the bodies after the survivors move on. While you watch, a group of Nords or bandits could show up, and the fight could get huge and chaotic. Magic could be flying as you dodge random firebolts. The chaos could attract a dragon by the end of the fight.
Does this system care about CR and balance?
No. Not one bit. The world "is what it is."
BX and old-school play are the same way.
Thinking "this is the game about my story" and "the adventure should be balanced so we can complete its story" is something out of the artificial world of structured play. Encounters are not balanced here. You need to sneak past fights, play dirty, save resources, be clever, and learn when to turn tail and run. You need a retreat plan for when it falls apart, and an idea on who carries fallen friends who can't make it themselves. Your plan can't rely on one spell or person. You need to play smart and understand the world does not care about you or your story.
But the world can show kindness. You could roll a friendly reaction roll from a group of kobolds who take pity on you as you just ran out of a room after a bugbear killed your cleric and thief, and you are out of hit dice to rest and wondering what you are going to do. If you can speak their language and part with a little treasure, they may help you get your fallen comrades back, since they hate the bugbears, too, and they would be happy to fight a skirmishing retreat for you as long as you promise to kill the warren of bugbears when you return.
This is a dynamic encounter that the DM turns into a story on the spot; it's not "pre-written" into the adventure but happens organically through the dice, tables, world, and luck. These types of stories are better than pre-written character stories, the stories written into adventures, and anything an adventure writer could think up.
When you get back to town, the temple says they can't raise your friends, but they can summon a high-level vicar from the city who could, for a generous donation, and perhaps, a problem they may need help with...
After all that, and with your friends returned to the living (or not, with new characters created), you set out again, thinking about those bugbears. The survivors of that fight remember, and a plan is made to deal with this problem once and for all. And you can be sure those kobolds will be close by, watching or perhaps helping again.
None of this is your prewritten character story or the adventure's narrative. All of this happens organically through the world simulation engine. And you can have this in 5E, any version of it that you play, for free if you adopt an old-school method of play, and that "world simulation engine" mentality to DM-ing. Again, you do not need BX to do this. While BX will make the failure conditions harsher and more dire, 5E can play an old-school game just fine and be just as lethal and dangerous.
The belief that BX is some magical panacea to solve all your problems with D&D is not entirely accurate. You may try it and love it. You may try it, hop games again, and end up missing 5E. What BX can teach us is that matters, and that can be used in any of our games, is the lost art of how to play an old-school game. What we do is recreate the old-school playstyle and keep that independent from the rules.
That "sandbox engine" we used to have before AD&D 2nd Edition was replaced by narrative railroading and the video-game-like progression of D&D 3.0. Narrative games are easier to DM and sell adventures for; they will have a bigger audience, so there is a financial incentive to ship them. It is easy to sell a game with a predictable, reproducible, pregenerated experience that plays like a theme-park ride every time, for every group. It is insanely hard to ship a game that delivers compelling, easy-to-manage, sandbox play.
But once you learn, a new style of play and types of interactive worlds are open to you. Your creativity goes from slightly tweaking published adventures to building living worlds.
You can play an old-school game in your game of choice.
You do not need to change the game.
You just need to change the way you think about it.
