What is a common contextual opener for traditional stories?

The phrase "Once upon a time" serves as a quintessential contextual opener for traditional stories, particularly those in the fairy tale and folktale genres. This phrase is universally recognized as a signal that a narrative will unfold, often transporting the audience to a setting in a distant time and place, fostering a sense of wonder and anticipation. This opening phrase establishes a narrative framework that encourages imagination and captivates listeners, inviting them into the world of the story. It creates an expectation of magical events and characters, setting the stage for the unfolding plot. Other options might also introduce narratives in different contexts, but "Once upon a time" is the most classic and widely accepted introduction for storytelling, especially in traditional narratives aimed at children.