Each of these can be measured. All events are known and can be assigned weights or probabilities that sum to 1.0, such that a definitive and calculable outcome is possible. Such definitive and calculable outcomes are certain in the sense that they can be predicted with some measure of confidence. This type of uncertainty or risk is very often insurable against disappointment, e.g. life insurance, fire and theft insurance, etc. Predictability and insurability take the guess world out of decision-making.
Economic participants are never subject to disappointment, because they know what the future holds.
Probabilistic uncertainty also provides a manageable methodology for models that draw conclusions about the real world. These models are often justified on the grounds that they eliminate subjective factors, they ease the mathematical and verbal exposition, and a world of disappointed expectations results in a level of turbulence beyond the skill of model builders to analyze. The Keynesians Versus the Monetarists Keynesians believe that the future is not measurable or known in any probabilistic sense. But while the past may be known for certain, the future is not. Economic participants will always hold some idle money balances for precautionary purposes.