The consolation of fairy stories, the joy of the happy ending: or more correctly of the good catastrophe, the sudden joyous "turn" (for there is no true end to any fairytale): this joy, which is one of the things which fairy-stories can produce supremely well, is not essentially "escapist," nor "fugitive." In its fairytale--or otherworld--setting, it is a sudden and miraculous grace: never to be counted on to recur.--J. R. R. Tolkien, "On Fairy Stories" (evangelium = gospel)
It does not deny the existence of dyscatastrophe, of sorrow and failure: the possibility of these is necessary to the joy of deliverance; it denies (in the face of much evidence) universal and final defeat and in so far is evangelium, giving a fleeting glimpse of Joy, Joy beyond the walls of the world, poignant as grief.
The peculiar quality of the "joy" in successful fantasy can then be explained as a sudden glimpse of the underlying reality or truth. It is . . . a "consolation" for the sorrow of this world. . . . But in the "eucatastrophe" we see in a brief vision that the answer may be greater--it may be a faroff gleam or echo of evangelium in the real world.
HT: Jerram Barrs