The predictability of an event or a quantity depends on several factors including; how well we understand the factors that contribute to it, how much data are available and
whether the forecasts can affect the thing we are trying to forecast.
A key thing is knowing when something can be forecast accurately, and when forecasts will be no better than tossing a coin. Good forecasts capture the genuine patterns and relationships which exist in the historical data but do not replicate past events that will not occur again.