An aeronautical engineer can predict reliably that “If you design a wing like this, then this plane will be airworthy, but if you design it like that, then it will never get in the air.” If you were to build a bunch of airplanes according to each set of specifications, you would discover that he or she is almost always right. This is actual expertise...
Our so-called experts in public policy talk a good game, but in the end are no experts at all. They build castles of words, and call it knowledge.