I wrote before about differences between what I called “Superpowers” type fantasy and “mysterious and wonderful” type fantasy. Just now, I was reading here about the difference between high fantasy and low fantasy. Basically, it says high fantasy takes place mostly in an alternate fantasy world where either they start out in the mundane world and then go to another place (Narnia Tales), or the alternate fantasy world is within the mundane world (Harry Potter), or the whole of the story is in the fantasy world (Lord of the Rings*). Low fantasy takes place in a real-world environment.
My stories tend to blur the line. By the definition, my story The Sacred Key is yo-yo fantasy. Most of the story takes place in the real world, so I guess it should be considered low fantasy, but several scenes take place in fantastic places (including another planet and the elemental plane of furniture).
In either case, it’s a very common trope in fantasy when the main characters start out in the real world and then they learn some magic secret which changes their life and either takes them to a fantasy world (whether it be within the real world or elsewhere), or makes the real world (at least sometimes) seem like a fantasy world. In C.S. Lewis’ The Lion, the Witch, and the Wardrobe, the four children come back from Narnia and find that their uncle has also been there. He was in on the secret. It works well to have one or two characters in the normal world be in on the secret, but if a lot of people know about it then it spoils something. The secret starts to seem like something normal which the main characters had been unfairly left in the dark about. It loses its magic.
Typically, magic is considered to be the primary thing that makes fantasy what it is. I agree, but I would say that the second definition of magic is just as important to fantasy as the usual definition. It seems to me that some stories leave out the sense of wonder. Even in the Lord of the Rings which takes place completely in its fantasy world, the hobbits begin the story in their own little world and then venture out to new places and discoveries. There’s a radical change when the characters in fantasy stories discover the story’s magic. It’s what the story is about. “Keep it secret, keep it safe**.”
*Although, as the wikipedia article mentions, JRR Tolkien argued that The Lord of the Rings took place in the real world in some pre-ancient time. Ironically, despite being the most iconic high fantasy epic story, the author claims it doesn’t fit the criteria of high fantasy at all.
**safe? Ha! that’s a funny word when it’s always precisely what leads into danger.