Jack Frost has never been something for people to believe in. He is the result of giving a phenomenon (cold weather, in this case) human-like qualities. This is a literary (rhetorical) device known as personification. Rise of the Guardians took it a step further and imagined Jack Frost as an actual person. Jack Frost is as "Believed in" as Mother Nature.Here's what is on my mind: I was watching Rise of the Guardians with my little sister, and I thought, wait, if nobody believed in Jack Frost until 2012, then how did the expression "Jack Frost nipping at your nose" come around?