I have always wondered why fairy tales so commonly started with that phrase, well after some thinking on my part I have my thoughts, (though I would love to hear your ideas below in the comments)
Well okay, so what if it is all a sort of trigger word where you automatically think of several different fantasies aspects and therefore you don’t need to spend much time actually describing the world, and you can focus more on the story at the surface.
Or on the trail of a third thought, perhaps it is a way to preserve a sense of timelessness, I mean if you think about once upon a time is way more intriguing than hearing,”On May 2nd, 2015, a fantastic story occurred…” Because it is so accurately dated that someone could just google the date and it sort of destroys the mist of fantasy.
Either way, those are just my ideas, what are yours? Do you write any stories beginning with once upon of time? Let me know in the comments below!