Why do people seriously believe in vampires/fairies and mermaids?

i dont have anything against pepole that believe in that kinda thing but honestly why would you go on yahoo anwsers and ask how do you become a vampire or mermaid or whatever seriously if you become a mermaid post a pic and prove the rest of us sane people wrong or something and im positive vampires dont exist.they are fictional creatures that make good story lines and movies if you really and truly believe in this stuff then my suggestion would be to 1 prove it exist and 2 get some help