is for VERISIMILITUDE
I have said before that I believe Tolkien's "On Fairy-Stories" (1947) is one of the most (fine, I really think the most) important pieces of theory for the practicing mythopoet. He gives us the concepts of sub-creation and secondary belief to describe the enchantment of mythic literature (or fairy-stories). The sub-creation enchants its readers by eliciting their secondary belief (in contrast to willing suspension of disbelief). The secondary belief of readers in a sub-creation depends on its verisimilitude. Verisimilitude is what elicits secondary belief and thus enchants. Without it, fantasy falls flat. Understanding Tolkien's point about verisimilitude, and then pondering deeply what it might mean for you and your audience, in particular how to sustain and not strain or break it, is worth your time if you haven't done it. If you don't have a copy of it in something that you already own, get yourself a paper or electronic copy right away. Read, ponder, repeat.