1. the DM describes a scene.2. the players express their actions.3. the DM describes the effects of those actions.
And return. The module presupposes that (3) is pre-planned, which means that options under (2) must be minimised to where the players can only do what's expected of them. This is why the dungeon is so practical for established structured game play, because there ARE only a few things that can be done at any specific time in the dungeon that can affect procedure (3) ... simplifying the game so that even kids can run it.
Once the game moves thematically out of the dungeon, to where the players engage in a story arc that requires, say, the rescue of a princess or the restraint of a wizard attempting to end the world, (2) has to be further controlled in order to assure that expected (3) results are still those the DM has pre-planned. This is called "putting the campaign on rails," in the sense that whatever the players give as an answer to (2), (3) is always the same. Always. Any deviation from the desired procedure for (2) creates negative consequences for the players until they recognise they should have done "this" and not "that," whereupon they do what's wanted and the adventure continues as pre-planned.
If, on the other hand, the game is run so that there is no pre-planned (3), then there need be no pre-planned (2). The DM need then only be concerned with (1) ... since the procedures of (2) and (3) have no fundamental effects upon the substance of (1).
All right, granted that's probably confusing. I'll give an example. I make a world that consists of you, a dog and a store. You're expected to take your dog to the store, so that I can say your dog pees on the store's floor and you get into trouble. If you take your dog somewhere else, that's no good, you have to go to the store. If you attempt to curb your dog, or tie the dog outside, that's no good, because I need the dog to pee in the store if the next series of events take place. Therefore, if you curb your dog, I have to make the dog bark until you do what I want. If you try to go somewhere other than the store, then I have to close everything until you go to the store, or make everything else so boring that you go to the store out of desperation.
On the other hand, if I don't care where you go, or what you do with your dog, then the actions you take of your own accord must, to support the game's functional procedures, produce previously unforseen consequences that I must invent in the present, directly from statements you've made about your dog — which I cannot know prior, because you haven't said them yet.
Playing this way, it means that as DM, I don't make the adventure. You make the adventure. But ... once you've taken an action, then I'm free to invent consequences to that action which, in turn, I can describe and to which you must take further actions.
Say, for example, (1) I describe a dungeon; (2) You state your desire to go to that dungeon; (3) The dungeon plays out as we'd expect. You're still the cause. You're still running the play. I'm reacting to your statements, while you react to my dungeon. This is fundamentally the same sort of play that is expected to occur in a common pre-packaged module ... which helps explain why it's so difficult to describe a "sandbox." Mostly because we tend to define a sandbox as what it isn't, rather than what it is. There's nothing about a sandbox that says it can't include all the facets of The Keep on the Borderlands as written. That needs to be understood.
It must also be understood that when you deviate from that common procedure, you're still in control. That doesn't mean your actions can't be pre-determined ... because you're human and we can certainly expect you to do certain things. But it does mean that the doing of those things is on you, and not on the DM.
For example. Bilbo is walking through a tunnel when he finds a gold ring laying on the ground. He chooses to pick it up and put it in his pocket. What player would not do the same? We DMs can be fairly sure that if we put a ring on the ground in front of a player, the player will pick it up. For future reference, we can call this "fishing."
More often than not, players won't question the effects that come from the actions they take. Bilbo certainly did not, and more importantly, underlined for emphasis, could not. No one could. The repercussions of Bilbo's finding of the ring reach far past the story being told about Bilbo, as we know too well. The fact of this makes it all the more likely that Bilbo, and any player, would certainly pick up the ring once it's seen.
Tolkein wanted the incident to occur in order to build a series of events that acted as effects to the cause. Of course, the earlier cause is that the ring abandons Gollum, and the cause before that is that Smeagol kills Deagol for possession of the ring, with the cause before that being that a battle left the ring lost in a river, and before that being that Isildur refused to destroy the ring in Mt. Doom and so on, going back to the making of the ring and before that Sauron's reason for making the ring ... and perhaps the fact that Sauron's mommie didn't let little Sauron have a puppy when Sauron was five. Who knows?
What matters is that once Bilbo picks up the ring, Bilbo has no control whatsoever upon the events that arise from that. These events are effects ... and once put in motion, the various characters in the narrative must deal with the effects as they come. To make it a good story, Tolkein has to be very, very careful to keep his fingerprints off the events, so that they seem to come logically one after another, without the heavy-handed guidance of the writer ruining everything.
The DM must also arrange the effects likewise. The players take an action, there are unforseen consequences for that action ... and a series of events, utterly unexpected and most desirably for the DM, undesired for the players, begin to accumulate beyond control.
My players in the online campaign opened up the tomb at Mimmarudla and some died fighting the beetles. Then the party went back, with new members, and killed the beetles. They found a door, and the means to open the door, and naturally went through the door with no more concern about the future than Bilbo had in picking up the ring. By opening the door, the players woke up an evil that had been sleeping for 900 years. They ventured into the dungeon, killed a few bad guys and walked out, limp and hurt and all alive, with a little treasure, some found objects and a book.
No problem. Standard D&D fare. In common practice, the dungeon is supposed to sit there, waiting for the players to return when it's damn convenient. After the first foray out to the Caves of Chaos, the goblins, orcs, ogres and so on don't send for their cousins around the neighbourhood, triple their numbers and attack the keep, do they? The next scene isn't the players fighting for their lives on the parapets, surrounded by humanoids, trapped in the keep and trying to keep the monsters at bay. No, the next scene is that the players rest up, restore themselves to full and return to the Caves, where nothing has fundamentally changed. All the monsters sit tidily in their rooms, where they belong.
That's not what I did with the Mimmarudla party. No, the evil emerged from the dungeon after the players left, and did not attack the party. No. They attacked farmers who were on the edge of the civilised area. They killed children and other innocents. And the party, understandably, blamed themselves.
And here again, we have a dilemma. No one knows the party had anything to do with it. The party can simply slink away ... but of course, that's the coward's route and even the most boorish of gamers don't like that label. They can own up ... but, again, Medieval game world, not a liberal mindset among authorities. That's one to hesitate on. Option three? Go back and fix it themselves. Except that now, with evil bad things running all over the neighbourhood, could be there are too many for a party of 1st levels to handle.
Yep, horns all round. Even though the party is perfectly safe in Stavanger, unharmed, healing themselves and completely innocent as far as the world's concerned.
This is the benefit of having the players set things in motion, that differs greatly from the common pre-packaged module. If the Tomb of Horrors kills you, first time in, well, it's the module's fault. It's the DM's fault. It's the fault of not being ready, or familiar, or high enough level. But you are not responsible. Not you.
Is Bilbo responsible? Not for a long time. Never occurs to him, not until long after his 111th birthday. But eventually, as the consequences multiply, he regrets picking up that ring. He can argue it, say that anyone could have picked it up, that he's completely innocent ... but inevitably, those excuses aren't enough. Inevitably, the only thought that's left is the wish that he hadn't gotten the ball rolling.
Do we think that the moment the ring hit the magma in Mt. Doom that Sauron had time to have his regrets for putting the original plan in motion? For making the ring in the first place. Was there time? I like to think there was.
So here's an emotion that gets lost in the mix of explaining what playing is: regret. Not fear, not resentment, not demanding the DM play "fair," etcetera ... but the simple fact of a player wishing he or she hadn't done something they definitely did. Most of the time, this consists of throwing the dagger and missing. "Damn, that was my last dagger." But there's a deeper regret. One that transcends a momentary failure from an unfortunate decision within a bad situation. No, no, I'm speaking of a bigger mistake. One that you never, ever get over.
I think we've all had them. And that as I write this, it's hard to push that regret from the reader's mind, just at this moment. Kind of floats there, doesn't it?
This is the level the game can be played on ... and played on fairly, without having to resort to railroading or forcing the players to take an action that fulfills a pre-set purpose. No, it's possible to observe the players practicing complete and utter free will, figure out dozens of possible consequences for their actions and then go with the one that will cut closest to the player's bone ... one that puts them in absolutely no danger whatsoever, but which feels like absolute shit.
One that makes them feel like they shouldn't have bit on that hook, which in no way looked like a hook at the time ... as they feel their slimy little bodies being hauled out of the water, while a small wooden club is raised over their head.