In a way macro economics seems like string theory to me: it's a struggle to grasp what is being claimed but success in that effort doesn't help determine if it is correct. Still, there are sometimes insights that resonate:

The first half of the Depression was a failure of right wing economics, as it was conceived at the time. The second half was a failure of left wing economics, circa 1935. If a single screw-up was capable of creating a Great Depression, we would have had many of them. Instead, this 12 year Depression was three times as long as any other Depression in American history.

The current recession (which was also caused by a failure of both right and left wing ideas) may end up being the second longest, at least if we measure it from the onset to the point where unemployment falls below some reasonable figure like 8%. But at least right-wingers no longer believe in the gold standard, and left wingers no longer support the NIRA. So we won’t have another Great Depression. We are making all the same mistakes, but in much milder forms.

Like politics and religion - and string theory - economics is mysticism. Beliefs can be strong and offensive to other faiths. It is impolite to discuss such things at the dinner table. It's pub chatter at best.

Economists have rarely claimed the role of kings, and, in many respects, they recognize their own limitations. Nonetheless, economists must appreciate the waste of massive intellectual energy as their best and brightest have chased intellectual puzzles that emerge from a flawed abstract understanding. It is little wonder that so much of what economists have said, and say now, is exposed as irrelevant and essentially useless.

Economists are embarrassed by their inability to offer ‘scientific’ explanations for the 2008–9 crises or to advance suggestions for reform. And for the few who have dared enter the political dialogue, the arguments seem to differ little, if at all, from the nostrums offered three-quarters of a century past by Keynes and his converted disciples. It seems as if, for economists, the whole post-Keynesian epoch must be judged to be a sequence of lost generations from whom no value product emerged at all. . .

Unfortunately, economists, generally, failed to understand that aggregate variables that may be measured with tolerable accuracy ex post may not be variables subject to control, directly or even indirectly. The fundamental misconception here lies in the understanding of what ‘the economy’ is. The ‘economic problem’ is not (despite Lionel Robbins) an engineering problem that may be defined simply as the allocation of scarce resources among alternative uses. The economy, in some inclusive definitional sense, is perhaps best described as an order that consists of an interlinked set of exchanges, simple and complex, from which outcomes emerge that may in some respects be meaningfully measured but that cannot be chosen, and thereby controlled, by concentrated decision takers.

The false conceptualization here is, of course, exemplified in the failure, both in theory and in practice, of the grand socialist experiments of the twentieth century. What remains missing, however, is a general recognition by economists themselves that their mind-set, when confronted with challenge, has not escaped from the engineering mentality. There has been little or no spillover from observation of events to the analysis by the putative scientists in the academies. It is not, therefore, surprising that the policy objectives and implementation are basically the same as those advanced by the Keynesians of midcentury.

Economists do not really understand what they are doing as they seem forced to make efforts to control aggregate variables that are not controllable in any direct sense. For example, the rate of employment (or unemployment) cannot readily be shifted by governmental mandate. At best, small and peripheral changes may be made while the emergent aggregate generated by the working of the large and complex economy remains stubbornly immune, or worse, to wrongly conceived reform efforts.

Many of the posts here are in the Natural Systems category and seek to illuminate some small segment of generally incomprehensible subjects, the muck and mystery of life. The engineering approach to natural systems has always seemed crushingly stupid to me. It was dull minded boys and girls with vicious temperaments poking cornered beasts with sticks just to hear them howl in pain. These sadists often claim to have admirable motives, but honesty is seldom one of their virtues. At best we get death bed confessions of malfeasance:

People who are raised in the industrial world and who get enthused about systems thinking are likely to make a terrible mistake. They are likely to assume that here, in systems analysis, in interconnection and complication, in the power of the computer, here at last, is the key to prediction and control. This mistake is likely because the mindset of the industrial world assumes that there is a key to prediction and control.

I assumed that at first too. We all assumed it, as eager systems students at the great institution called MIT. More or less innocently, enchanted by what we could see through our new lens, we did what many discoverers do. We exaggerated our own ability to change the world. We did so not with any intent to deceive others, but in the expression of our own expectations and hopes. Systems thinking for us was more than subtle, complicated mindplay. It was going to Make Systems Work.

But self-organizing, nonlinear, feedback systems are inherently unpredictable. They are not controllable. They are understandable only in the most general way. The goal of foreseeing the future exactly and preparing for it perfectly is unrealizable. The idea of making a complex system do just what you want it to do can be achieved only temporarily, at best. We can never fully understand our world, not in the way our reductionistic science has led us to expect. Our science itself, from quantum theory to the mathematics of chaos, leads us into irreducible uncertainty. For any objective other than the most trivial, we can't optimize; we don't even know what to optimize.

I've used that quote many times and it bears repeating. See This Year's Girl where it was used in a discussion of geoengineering. It isn't just that you can't engineer what you can't measure and predict, it is also that there is something distasteful about the desire to do so. IMV it is an aesthetic as well as an intellectual failure.