Lots of ideas like this in Pratchett, he talks about urban legends that really happen in Witches Abroad, and stories as living things that try and twist people into their forms, rather than the other way around. Belief is so strong on the Discworld that it can create gods, so if you get a myth or legend or fairytale enough belief, it will become true. I can't think of specific incident off the top of my head except the ones already mentioned, but he talks about this kind of thing a lot.