'i don't hold with paddlin' with the occult,' said Granny firmly. 'Once you start paddlin' with the occult you start believing in spirits, and when you start believing in spirits you start believing in demons, and then before you know where you are you're believing in gods. And then you're in trouble.'
'But all them things exist,' said Nanny Ogg.
'That's no call to go around believing in them. It only encourages 'em.'

Granny Weatherwax
Terry Pratchett