I don't usually like broad-statement declarations about writing, but bear with me here. Writing is about limits. More specifically, it's about the limitations we impose on ourselves. Even the act of writing itself is a limitation—there are things you can't do with words that you can do with, say, images. Likewise the decision to write a "short story" instead of a poem or an essay. And then, once you're in the story, the choices you make limit what you will write about, and how you will write it. We accept this, of course, or even demand it: after all, storytelling has rules, it has forms, it has modes.
For example: the "rules" of first-person are different from third-person. Genres have various accepted OKs and Not OKs. Tense matters, as do syntax, margins, spacing. All of it does to varying degrees. So we could say that every story written is a product of the limitations the writer has placed on it, either consciously or unconsciously. This is common sense, maybe, but it's something I try to remind myself of when I want to push a story into new places.
So limitations matter, because they're a necessary function of creating something. But the constraints of a particular style don't have to be set in stone. The rules might be the rules, and the restraints of your choices might engender a certain kind of story development, but who's to say that you can't change what you're doing? Stories are best when they surprise us, which maybe means that we, the people doing the writing, first need to surprise ourselves. We can do this by choosing our own constraints.
After all, we already limit ourselves whenever we start, write, and finish a story, so why not just embrace the idea? A popular method, especially in poetry, is the Oulipo exercise. These exercises were devised by French mathematicians to create very specific formal constraints—for example, a "snowball" poem might start with a single word before adding one to each line; or, it could be structured so each line is made up of progressively longer words. The idea is that constraint makes you write something you wouldn't normally write.
Oulipian exercises are often complicated and based in math (look up the N+7), but the idea of constraint—that's simple. That makes sense. I used to make myself write scenes in 50-word segments (exactly 50 words), and only later would I link them up and expand them into something longer. What did this get me? An appreciation, maybe, for technical aspects of storytelling that I hadn't considered before. Writing to an exact word count made me really weigh each word and every phrase, and encouraged me to relearn the importance of nouns, verbs, concise descriptions. I ended up with tighter, leaner stories that did more with less, and which often ended in radically different places than I originally thought they'd be. And that's the idea, right—to see what you can change, whether structurally, generically, formally, etc., in order to make the story do something new.
So by all means, write that genre-mashup that shifts tense and POV at the drop of a paragraph. Or, maybe, start slower: experiment with a single unexpected shift in point of view. Mess around with tense—what does a new layer of narrative time imply about the story? Withhold vital information, or start the story with the ending and work your way backward. Structure around a countdown.
Try to challenge yourself as a way to surprise yourself. It might help to think of your self-imposed constraint as an anchor, or a safety net. Constraint is structure, after all, and you can rely on it. If nothing else, give yourself the permission to get weird. Embrace new constraints, or constraints that you didn't think fit in the story as you originally envisioned it. If you're like me, you'll be surprised—and pleased—at what you end up with.