It had always seemed to Emily, ever since she could remember, that she was very, very near to a world of wonderful beauty. Between it and heself hung only a thin curtain; she could never draw the curtain aside - but sometimes, just for a moment, a wind fluttered it and then it was as if she caught a glimpse of the enchanting world beyond - only a glimpse - and heard a note of unearthly music.

L. M. Montgomery, Emily of New Moon

"I coined the word 'eucatastrophe': the sudden happy turn in a story which pierces you with a joy that brings tears (which I argued it is the highest function of fairy-stories to produce). And I was there led to the view that it produces its peculiar effect because it is a sudden glimpse of Truth, your whole nature chained in material cause and effect, the chain of death, feels a sudden relief as if a major limb out of joint had suddenly snapped back. It perceives – if the story has literary 'truth' on the second plane (....) – that this is indeed how things really do work in the Great World for which our nature is made. And I concluded by saying that the Resurrection was the greatest 'eucatastrophe' possible in the greatest Fairy Story – and produces that essential emotion: Christian joy which produces tears because it is qualitatively so like sorrow, because it comes from those places where Joy and Sorrow are at one, reconciled, as selfishness and altruism are lost in Love."

― Letter 89

In his On Fairy-Stories Tolkien describes eucatastrophe further:

"But the 'consolation' of fairy-tales has another aspect than the imaginative satisfaction of ancient desires. Far more important is the Consolation of the Happy Ending. Almost I would venture to assert that all complete fairy-stories must have it. At least I would say that Tragedy is the true form of Drama, its highest function; but the opposite is true of Fairy-story. Since we do not appear to possess a word that expresses this opposite — I will call it Eucatastrophe. Theeucatastrophic tale is the true form of fairy-tale, and its highest function.

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 fairy-tale): this joy, which is one of the things which fairy-stories can produce supremely well, is not essentially 'escapist', nor 'fugitive'. In its fairy-tale—or otherworld—setting, it is a sudden and miraculous grace: never to be counted on to recur. 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, if you will) universal final defeat and in so far is evangelium, giving a fleeting glimpse of Joy, Joy beyond the walls of the world, poignant as grief.

It is the mark of a good fairy-story, of the higher or more complete kind, that however wild its events, however fantastic or terrible the adventures, it can give to child or man that hears it, when the “turn” comes, a catch of the breath, a beat and lifting of the heart, near to (or indeed accompanied by) tears, as keen as that given by any form of literary art, and having a peculiar quality."

― On Fairy-Stories

“I call it Joy. 'Animal-Land' was not imaginative. But certain other experiences were... The first is itself the memory of a memory. As I stood beside a flowering currant bush on a summer day there suddenly arose in me without warning, and as if from a depth not of years but of centuries, the memory of that earlier morning at the Old House when my brother had brought his toy garden into the nursery. It is difficult or find words strong enough for the sensation which came over me; Milton's 'enormous bliss' of Eden (giving the full, ancient meaning to 'enormous') comes somewhere near it. It was a sensation, of course, of desire; but desire for what?...Before I knew what I desired, the desire itself was gone, the whole glimpse... withdrawn, the world turned commonplace again, or only stirred by a longing for the longing that had just ceased... In a sense the central story of my life is about nothing else... The quality common to the three experiences... is that of an unsatisfied desire which is itself more desirable than any other satisfaction. I call it Joy, which is here a technical term and must be sharply distinguished both from Happiness and Pleasure. Joy (in my sense) has indeed one characteristic, and one only, in common with them; the fact that anyone who has experienced it will want it again... I doubt whether anyone who has tasted it would ever, if both were in his power, exchange it for all the pleasures in the world. But then Joy is never in our power and Pleasure often is.”
― C.S. Lewis, Surprised by Joy: The Shape of My Early Life