It doesn't stop being magic just because you know how it works.

...it is well known that a vital ingredient of success is not knowing that what you're attempting can't be done.

I [...] vowed that rather than let Alzheimer's take me, I would take it. I would live my life as ever to the full and die, ­before the disease mounted its last ­attack, in my own home, in a chair on the lawn, with a brandy in my hand to wash down whatever modern ­version of the "Brompton cocktail" some ­helpful medic could supply. And with ­Thomas Tallis on my iPod, I would shake hands with Death.

Life doesn't happen in chapters - at least, not regular ones.

Bringing about Armageddon can be dangerous. Do not attempt it in your own home.

Ankh-Morpork! Pearl of cities! This is not a completely accurate description, of course — it was not round and shiny — but even its worst enemies would agree that if you had to liken Ankh-Morpork to anything, then it might as well be a piece of rubbish covered with the diseased secretions of a dying mollusc.

Be careful what you wish for. You never know who will be listening.