This is a good one:
... you don’t write a story, you write part of one. A story should be a slice of your setting, a piece of the history of that setting, a small and interesting part of a much larger potential. It should have characters who are not sprung into being at the start, but are created and written so they feel like they have pasts and futures outside of your story. Everything should feel large, no matter how short the story is.
Martin Scorsese once put it this way: Cinema is a matter of what's in the frame and what's out of it. Selectivity is what makes mere sensation or matter into art: where to start, how long to follow the action, what note to leave everything on. (One of the first things I think about with any story is that final emotional note: how do I want you to feel about it when you close the cover?)
From this sentiment stem most of my complaints about the way fiction and entertainments are ceasing to become stories and turning more into environments or continuua. The more you try to prolong something, the greater the risk of it devolving into eye-rolling soap opera. You pick a starting point, a pace for the whole, and an angle of departure for a reason: they add up into the complete experience. And the whole point of that complete experience is to provide other people for a starting point for whatever they come up with. It's not that it's impossible to do that with something that's been spun out into a multi-phase Marvelverse; it's just harder than it needs to be.
One analogy I came up with for this works like so. You're not a librarian or an encyclopedist, trying to anthologize and systematize everything that could possibly end up under the roof of your story. You're a DJ. You're curating the things that work best in the context of the party you're working, making elements flow into each other. You're not putting together a card catalog or an encyclopedia. You're making one of those seamless dance-mix releases. They don't have to include everything, just the bits that you know get peoples' feet and booty moving.
I shouldn't make it sound like continuum-type storytelling has nothing to offer. It's just that all the things it offers are secondary elements, not prime movers: setting, backstory, ambience, et al. Most of us find encyclopedias or libraries useful, but not as something to just consume end-to-end. A club mix of a given genre (lounge groove, drum 'n bass, what have you) isn't comprehensive, but it isn't meant to be. Comprehensiveness isn't what storytelling is about.
Many authors have at some point this ambition to stuff everything they possibly can into a single all-inclusive Story. They don't want to feel hemmed in by choices. But a story is an embodiment of the choices made by the author, and when you avoid making those kinds of choices, you don't really have a story anymore. And the fact that a story encompasses more, or contains more, is not a sign of its quality, just its ingredient list. Better a few good tracks than a whole crateful of duff ones.