...the proliferation of luminous fungi or iridescent crystals in deep caves where the torchlessly improvident hero needs to see is one of the most obvious intrusions of narrative causality into the physical universe.

It is a popular fact that nine-tenths of the brain is not used and, like most popular facts, it is wrong. Not even the most stupid Creator would go to the trouble of making the human head carry around several pounds of unnecessary gray goo if its only real purpose was, for example, to serve as a delicacy for certain remote tribesmen in unexplored valleys.

They were indeed what was known as 'old money', which meant that it had been made so long ago that the black deeds which had originally filled the coffers were now historically irrelevant. Funny, that: a brigand for a father was something you kept quiet about, but a slave-taking pirate for a great-great-great-grandfather was something to boast of over the port. Time turned the evil bastards into rogues, and rogue was a word with a twinkle in its eye and nothing to be ashamed of.

A weapon you held and didn't know how to use belonged to your enemy.

It was Carrot who'd suggested to the Patrician that hardened criminals should be given the chance to 'serve the community' by redecorating the homes of the elderly, lending a new terror to old age and, given Ankh-Morpork's crime rate, leading to at least one old lady having her front room wallpapered so many times in six months that now she could only get in sideways.

But I think you have a right to know what it is you’re not being told.

It's still magic even if you know how it's done.