Brandon Sanderson
Chapter Eighty-One - Part One
Prophecy
I wasn't certain how I wanted to treat prophecy in this book. On one hand, it's a staple of fantasy books—and my goal in this series was to take the fantasy staples and turn them upon their heads in a way that hadn't been done before. That meant I needed to include and use them, and so I did. In book two, the prophecies turned out to be false, and Ruin used them to trick Vin into releasing him.
However, the fact that he twisted the prophecies left me with the implication that they had once been true. What does that mean, though? If you look at prophecies in our own religions, very few of them are used like fantasy prophecies. In fantasy novels, it seems like prophecies are intentionally obscure, abstract things intended to confuse people and act as some kind of twisted guidebook for the hero to live his life. Yet, in modern religion—specifically Judaism and Christianity—prophecy is more general. Prophecy in these religions means things like "in the end, the faithful will win." They're general or symbolic. Of more use to the population as a whole, rather than applying to one distinct individual.
Sazed and Tindwyl have a great discussion about this in book two. Regardless, I make use of the prophecies here in the final book. As far as I'm concerned, they were given to the original Terris people by Preservation as a means of maintaining hope. They were a promise—a hero will come; that hero will protect you. Have faith.