"It was probably some wonderful organization on the part of Nature to protect itself. It saw to it that everyone with any magical talent was about as ready to co-operate as a she-bear with toothache, so all that dangerous power was safely dissipated as random bickering and rivalry. There were differences in style, of course. Wizards assassinated each other in draughty corridors, witches just cut one another dead in the street. And they were all as self-centred as a spinning top."
Terry Pratchett - Wyrd Sisters: (Discworld Novel 6)