I've been reading old fairy tales, trying to reshape and recast a couple into short stories. It's an interesting process. Some of the cardinal dos and don'ts of writing don't seem to apply to the fairy tale, leaving both quite a job of reinterpretation and the question of whether or not these rules are universal or even necessary. This is not the occasional lapse, although the fairy tales that endure seem to have a greater degree of conventional elements. This is a continuous appearance in stories that are archetypal, ageless and endlessly fascinating.
Coincidence abounds; luck saves the hero. Outside benefactors are common, giving gifts that are just what the hero requires or providing advice at just the right moment. Sometimes, the story jumps to another section with no apparent explanation - we're given to expect a tale about a boy promised to a mermaid who never reappears in the narrative.
On the other hand, the often subliminal rule of three is almost invariably made explicit in the fairy tale. There are three trials, three sections, three wise men to consult. Unlike in most modern fiction, where this is hidden, the fairy tale revels in the triad. Also, too, there is a sense of cosmic motivation, the world moving around the hero to some logic that maybe - just maybe - we could discern with the right mindset.