Your average witch is not, by nature, a social animal as far as other witches are concerned. There's a conflict of dominant personalities. There's a group of ringleaders without a ring. There's the basic unwritten rule of witchcraft, which is 'Don't do what you will, do what I say.' The natural size of a coven is one. Witches only get together when they can't avoid it.
Terry PratchettRead