According to Tolkien, all true fairy tales have four characteristics:
Fantasy - imagining unreal things but endowing them with "the inner consistency of reality"; both the quality of strangeness and wonder at the unreal and the “sub-creation” of an internally consistent secondary world are necessary. Fantasy involves “freedom from the domination of observed ‘fact’.”
Recovery - the ability to see things more clearly after experiencing the fantasy; this is a “regaining of a clear view,” which implies that we had it once and have lost it. Tolkien says recovery is “seeing things as we are meant to see them,” as things apart from ourselves. This can be fairly trite stuff, as when seeing something from a slightly different angle causes us to find it fresh again. But it is something more with creative fantasy - it can be dangerous, causing us to lose all of the cherished objects we have found in the ordinary view.
Escape - i.e., the fairy tale does not treat what is "real" as inevitable; it suggests alternatives, even (especially?) if the alternatives are genuinely impossible.
Consolation - the happy ending, or eucatastrophe (Tolkien's term); this is the moment of joy at deliverance from evil. Tolkien connects his concept of fairy tales to Christian theology (Tolkien was a deeply religious Catholic) by stating that the greatest eucatastrophe is the resurrection..