Economics at its base is group psychology, and humans are irrational and wildly unpredictable. A lot of economics writing depends on a rational human that actually doesn’t exist.

Hence why a lot of economics is speculative and should only really be applicable to specific cultures that are being studied, since cultural behaviors and expectations will effect economic behaviors and outcomes.

There’s a balance between data and interpretation in economics, which is why it’s a social science. There are disciplines like Austrian economics that discount quantitative analysis, but that’s as wrong as relying purely on quantitative analysis.

A human is irrational and wildly unpredictable, but groups of people (like most animals) are more easily predicted. While it's difficult to predict a specific stock, it's easier to predict trends given global situations, within a certain time frame, with enough information. The main problem becomes having access to such information. So much of the economy is global now, and behind closed doors, that information is unavailable or at a premium.

It works the other way too. If everybody believes that your model is correct, the chances are very good that its predictions actually become true.

That's the driving force behind a lot of religions and other traditions.