While politicians who like to defer responsibility to economists would want their electorate to believe otherwise, economists are not soothsayers. They are familiar with some ideal models for modeling economic systems of a few variables that may or may not hold up depending on the actual market conditions.

Economic forecasts are a bit like really bad weather forecasts - given a few variables and that nothing changes they may hold up.

But they cannot predict what will change and what effects it will have. Like the long term implications of internet.

For small systems with stable technologies like markets for a limited set of products some macroeconomic rules may hold up pretty well. But for large scale economies the economic decisions are as much political as fiscal, and the soundness of the decisions can be found out only in retrospect...