It was said that life was cheap in Ankh-Morpork. This was of course, completely wrong. Life was often very expensive; you could get death for free.
And what do you really do? asked Tiffany. The thin witch hesitatied for a moment, and then: We look to ... the edges, said Mistress Weatherwax. There's a lot of edges, more than people know. Between life and death, this world and the next, night and day, right and wrong ... an' they need watchin'. We watch 'em, we guard the sum of things. And we never ask for any reward. That's important.
