The mariners of the sixteenth century could not have imagined that people would ever cross the ocean in anything but a ship. Not only technological facts but also moral facts can seem impervious to change. In many sophisticated precincts into the nineteenth century, few objected to child labor, now almost universally scorned.
Even in the rare moments when people do perceive that civilization is about to change, and change radically, just what will change remains necessarily occluded. Think of the anxious literature of the Aztecs on the eve of the Spanish conquest, so full of apprehension and yet so profoundly unknowing at the same time.