Sorry, I meant that fantasy usually is in a unrelated-to-our-own fantastical world or it's in the real world (e.g urban fantasy), but the fact that magic exists and the reader "didn't know" about it must be explained (e.g Harry Potter, Dresden Files).
What's the alternative to not explaining here? Is it making the magic subtle/weak/uncommon enough that the answer is "you didn't notice, and this is plausible to claim"? If the magic is blatant enough and there's no explanation, the story becomes even less attached to reality than "there's a lot of magic but it's deliberately kept hidden".
