The purpose is to make a wish, but have the next poster grant it, but corrupt it (eg. poster1: I wish my feet had jet engines in them, poster2: granted, but you can't turn them off). He in turn must make a new wish.
I wish I could enough money playing jazz to quite my day job.
"The music business is a cruel and shallow money trench, a long plastic hallway where thieves and pimps run free, and good men die like dogs. There's also a negative side." -- HST