From Robert Solow's Nobel Address, in Stockholm, 1987:
The "neoclassical model of economic growth" started a small industry. It stimulated hundreds of theoretical and empirical articles by other economists. It very quickly found its way into textbooks and into the fund of common knowledge of the profession. Indeed that is what allows me to think that I am a respectable person to be giving this lecture today. Nevertheless I must summarize the outcome in a couple of sentences, so that I can move on to the more interesting questions about what is still unknown or uncertain and remains to be found out.
Just allowing for a reasonable degree of technological flexibility accomplished two things. In the first place, the mere existence of a feasible path of steady growth turned out not to be a singular event. A range of steady states is possible, and the range may even be quite wide if the range of aggregative factor-intensities is wide. There are other ways in which an economy can adapt to the Harrod-Domar condition, but it still seems to me that variation in capital-intensity is probably the most important.
Secondly, it turned out to be an implication of diminishing returns that the equilibrium rate of growth is not only not proportional to the saving (investment) rate, but is independent of the saving (investment) rate. A developing economy that succeeds in permanently increasing its saving (investment) rate will have a higher level of output than if it had not done so, and must therefore grow faster for a while. But it will not achieve a permanently higher rate of growth of output. More precisely: the permanent rate of growth of output per unit of labor input is independent of the saving (investment) rate and depends entirely on the rate of technological progress in the broadest sense. (emphasis mine)
Technological progress is a problem. They don't sell it in boxes. Policies designed to focus on saving, or consumption, don't accomplish much, except to keep politicians and pundits in business ("Vote for me, folks, and you'll soon be farting through silk!!")
Hard for politicians to admit, "The best thing we could do is create a setting where innovation flourishes, and is rewarded, and get the hell out of the way!" Even the word, "progress," has been stolen by those Luddites who call themselves "Progressives" but who in fact try to protect industry and hold back economic change. "Progress" is not building roads. Progress is individual humans thinking of new ways to use roads, and new products to move along those roads.
I am excerpting Solow, of course. Much of his real view has to do with stimulating effective demand, Malinvaud's famous theory of disequilibrium. But I do have to give Solow some credit for the way he concluded. A nearly Austrian riff, though he seems to approve:
When I read Robert Frost's lines from "The Black Cottage":
Most of the change we think we see in life
is due to truths being in and out of favor
it occurred to me at once that they sound altogether too much like economics. Some of that feeling is inevitable, and not necessarily to be regretted. The permanent substructure of applicable economics can not be too very large because social institutions and social norms evolve, and the characteristics of economic behavior will surely evolve with them. I believe also that part of the changeability of economic ideas on a shorter time-scale is our own doing. It comes from trying too hard, pushing too far, asking ever more refined questions of limited data, over-fitting our models and over-interpreting the results. This, too, is probably inevitable and not especially to be regretted. You never know if you have gone as far as you can until you try to go further.