Sometimes I wonder about things like the tooth fairy.  Who came up with this idea?  Why does this magical tooth fairy harvest children's teeth for money?  What does she do with all those teeth?  And where does she get all the money?  How did Hallmark not invent a holiday centered around this idea? 

Wikipedia says that the myth may be used to offer a reward to a child after a harrowing experience like losing a tooth.  No pain, no gain.  Another explanation is that some European folklore mentioned mythical creatures that would "perform useful tasks or exchange valuable treasures for things humans view as mundane or useless".  Money in exchange for teeth.  Clean house in exchange for nail clippings (my contribution; not in Wikipedia article).  Weird.  But the most compelling explanation is that it gives children a sense of faith in things that are unseen.  That's something I never really thought about before.  Maybe that can explain Santa Claus and the Easter Bunny.  Interesting.