For anyone who missed it, the title is a line from "Peter Pan".
The scene in which Tinkerbelle bravely drinks poison Hook left in the "medicine" (water in a flower cup) that Wendy left for Peter, before she was kidnapped by the pirates. So, Tink drinks the poison, to save Peter's life, and slowly, her light goes out. Peter cries, and starts repeating the abovementioned mantra, until eventually, everybody in Neverland (barring most of the pirates, and Hook, of course) takes it up, and restores Tinkerbelle to her rude, obnoxious, fairy-self.
See, when you say, "There's no such thing as ...." (you know, the f-word, I'm not gonna specify, for fear of one of them dropping dead somewhere), you kill them. Cos you gotta believe, for them to keep existing. For fairy balls to take place in fairy circles, and for children to see glimpses of pretty, shiny, flying things in forests, you gotta believe.
So, even though I haven't seen it myself, I'm not gonna say .... (you know, the l-word)... doesn't exist, cos in order for people to experience love, and find love in the world, you gotta believe in it.