Aliens don't always come from other planets--sometimes they come from other realities. That can include realities we're familiar with, like the worlds of storybooks.
In 1987, 24 years before Once Upon a Time, two producers from Who's the Boss?--a show that was itself built around mining the yawning cultural differences between blue-collar regular guy Tony Danza and high-powered career woman Judith Light--created a series based around fairy-tale characters brought into the real world and forced to act like normal, mundane humans. As in all version of this trope there are nosy neighbors, and strange phenomena and stranger behavior that have to be explained away every week to the accompaniment of an indulgent laugh track, so that the deception can persist from one week to the next, as the protagonists learn, very, very, slowly, to adapt.
In this case, Snow White, Prince Charming, step-mother Lillian, the dwarf Luther, and kids Thomas and Cory don't wind up in picturesque Maine, but Burbank--the town where stories like theirs are manufactured for television every day. This scenario emphasizes a sort of falseness to the habits and customs of aliens: they have sharp edges that need to be planed down and brought into line, because they should know how a toaster works, after all--doesn't everyone?
