Author of the acclaimed work Iceberg Risk: An Adventure in Portfolio Theory, Kent Osband argues that uncertainty is central rather than marginal to finance. Markets don't trade mainly on changes in risk. They trade on changes in beliefs about risk. In the process, markets unite, stretch, and occasionally defy beliefs. Recognizing this would make a world of difference in investing. Belittling uncertainty has driven a rift between financial theory and practice and within finance theory itself. It has misguided regulation. It has stoked the greatest financial imbalances.