When telling a story, you need some sort of common understanding with your audience. They need to understand the environment in which your characters and narrative exist. Actions have importance because of the relationships of characters, organizations, and concepts within the story. If this shared understanding doesn’t exist before the story begins, the storyteller must create it in some way.
Storytellers can handle this in a couple of ways. In the first, the storyteller strips down the story to the barest of essentials. In shorter forms, creating the environment can create real challenges. “Show, don’t tell,” might not work as well in flash fiction or even short stories because the story will end before it has room to explain. So any element not needed by the story gets ruthlessly cut out, so that the story has time and space to include the really essential bits.
Alternately, the story can occur in a pre-existing universe. This could include our own, but even so the story has to establish an environment with enough specificity that the audience can relate to the narrative, particularly if the perspective doesn’t match theirs. This could also include pre-existing fictional universes, so that the story dips into the realm of fan-fiction.
Think about Star Wars, one of my personal favorites. Generally speaking, a story in the Galaxy Far, Far Away doesn’t have to belabor the reader with explanations of the evil Empire, the noble Rebel Alliance, the self-sacrificing Jedi, the ferocious Wookiees, etc., unless the story really delves into one of those in great detail. The audience already has the necessary framework. With a few short strokes, the story establishes an emotional and intellectual context.
This can lead to issues based on derivative work or trademarks, so storytellers have to choose carefully. The “owners” of some universes sometimes encourage this storytelling and sometimes don’t. If money gets involved, things get very messy very rapidly.
So think carefully when constructing a story. Do you really need to set it in an existing universe (e.g. fan fiction)? Or do you have the room to explain somehow what the audience needs to understand while setting it in an original or real-life environment?
Or would constructing the narrative in an entirely different medium do a better job of showing without telling? Some stories work better as films and others as novels, but storytellers have so many more choices now in the media they can choose and so much more power as individuals.