Sourcery (Discworld, #5; Rincewind, #3)

by Terry Pratchett

I SAID NO. NOTHING IS FINAL. NOTHING IS ABSOLUTE. EXCEPT ME, OF COURSE. SUCH TINKERING WITH DESTINY COULD MEAN THE DOWNFALL OF THE WORLD. THERE MUST BE A CHANCE, HOWEVER SMALL. THE LAWYERS OF FATE DEMAND A LOOPHOLE IN EVERY PROPHECY.