Why Mainstream Economists Are Mostly Wrong

How could economists/experts get it (forecasting, policy prescriptions) so wrong?

This from Janus Lim of the World Bank (hat tip: Prof Antony Mueller) [bold emphasis mine, italics his]

It would seem that the current crop of modern macro models are not only ill-suited for prime-time policymaking in the developed world, they are also inadequate for the developing-country context. At some level, this is ironic. Developed economies are typically far more complex, with larger and more sophisticated product, financial, and labor markets. If anything, the relatively simple structure of DSGE models should be attractive to developing countries, since they are more likely to be successful in capturing the primary features of these economies.

Of course, it may well be the case that developing country policymakers are not quite ready for such sophisticated, state-of-the-art macro modeling tools. Perhaps so, but this seems to me to be a red herring. While ease of use is certainly relevant for capacity-constrained LDCs, the more important question to ask is whether such models can answer the questions foremost on the minds of developing country policymakers. If they can't, it matters much less that the developing world is not ready for them. It would be more that these models are not ready for the developing world.

For simplicity sake, the answer is because they substitute models for human action.

Prof Richard Ebeling writes,

The inability of the economics profession to grasp the mainsprings of human action has resulted from the adoption of economic models totally outside of reality. In the models put forth as explanations of market phenomena, equilibrium — that point at which all market activities come to rest and all market participants possess perfect knowledge with unchanging tastes and preferences — has become the cornerstone of most economic theory.