This is how Vetinari thinks, his soul exulted. Plans can break down. You cannot plan the future. Only presumptuous fools plan. The wise man steers.

—Terry Pratchett, Making Money

Although thought by a madman in the book, there seems to be truth in this quote. People often seem to think of the future as a coherent, specific story not unlike the one woven by the brain from the past events. Unpleasant surprises happen when the real events inevitably deviate from those imagined.