Unless we remember we cannot understand.
Curiosity is one of the lowest of the human faculties. You will have noticed in daily life that when people are inquisitive they nearly always have bad memories and are usually stupid at bottom.
Our easiest approach to a definition of any aspect of fiction is always by considering the sort of demand it makes on the reader. Curiosity for the story, human feelings and a sense of value for the characters, intelligence and memory for the plot. What does fantasy ask of us? It asks us to pay something extra.