Often they aren't, as with most macroeconometric measures. Most of physics does not attempt to understand why these quantum events occur but simply describes the aggregate behaviour of large numbers of events. As we begin to understand the low-level mechanisms, we will get to the true physics beneath the aggregates. Similarly, in economics we try to predict behaviour of aggregates of individual transactions. One may not be able to understand what drives the transactions by theorising based upon aggregates.
Parallels exist between markets and quantum mechanics.
The electron has no position or momentum until you measure it. When you measure its position, you disturb it, foregoing accuracy in measuring the momentum. A share of General Motors has no price until a buyer and seller exchange it, a discrete event. Similarly, you can predict interference fringes to many decimal places but which detector an individual electron will trigger in a dual slit interference experiment is unknowable in principle. The market is neither up nor down.