D&D is unique in terms of fiction, in that modules aren’t realized until a group of people play them. It can be useful to think about the process a module undergoes from being finished to being played.
A module begins its active life by being read by a GM. When reading the text, the GM automatically interprets, reacts, and visualizes the adventure. It’s important to understand that to the GM, their interpretation and understanding of the adventure is the actual adventure. As Rene Magritte says, “perception always intercedes between reality and ourselves”. This is to be expected, during reading the GM will create their own version of the adventure. It’s the job of the adventure writer to aid them in that process.
Like a short story, the adventure writer needs to convey the atmosphere and meaning of an adventure to the GM. Presumably, the players won’t read the module and only receive it secondhand. If a module is static and defines itself, the GM isn’t given room to improvise or create on their own, if there’s no expectation for the GM to interpret or be affected by the text then the GM is robbed of the ability to act as a storyteller. This is insane as the GM’s primary way of playing the game is to describe events or areas to the player. For this reason, it’s imperative the writer try to inspire the GM while providing room for them to personalize the adventure.
The players, presumably, will never interact with the text of the adventure directly (excepting read-aloud text, but that’s a different discussion). Their primary interaction they will have with the module is through the filter of the GM. At this point, the adventure exists as a shared creation between the GM and players with no party having the same interpretation or ownership of the story. While the GM provides descriptions and resolves rules, the player’s only method of interacting with the fiction is to declare the actions of their characters.
There’s a reason people hate railroads. It removes the player’s ability to create a story and forces them into the role of a passive actor who must jump through hoops to unlock the next scene. Railroads betray the distinguishing feature of TTRPGs, that the players can be authors of their own story. This isn’t to say that boundaries aren’t acceptable in an adventure. If I told my players that our campaign was set on a large island and their first action was to build a raft and escape to the mainland, I’d rightfully be a bit miffed. The intent is to provide meaningful choice, motivation, and maximal agency to the players. For all that this is common advice to new GMs, precious few modern adventures are written with this mindset.
Within the premise of the adventure, the GM must be given tools. “An army will arrive in 3 days to siege the dungeon.” is a static and self defined fact. “The army has these logistics, their objective is the dungeons wealth and they can move this many miles a day.” conveys the same goal (Adventure timeline) while providing the GM tools and a process for running the adventure. Rather than shaping reality to fit the adventure towards the neccessary event of the army arising, players and events must be given agency to interact with the fiction. The non-process and non-tool oriented nature of a conventional d&d “story structure” puts the onus of effort on the GM if the players ever meaningfully engage in the fiction by “Going off the rails” and becoming creative actors in the game.
And now we arrive at the adventure in its realized form when a plot takes shape. The GM is supported in conveying a situation in his own voice (I believe in you random GM) while the players are allowed to meaningfully engage with the setting. An adventure exists somewhere in between the two groups and takes forms that no module writer can hope to predict. The collaborative story that springs from the table, the plot, is the only thing that matters. The module itself will always be lacking. I can provide everything but the plot, that you have to create yourself.