There is much talk of how Covid is putting pressure on the NHS. Such talk, however, often misses an important fact - that although NHS capacity is more or less fixed in the short-term, it is certainly not in the long-run. And past political choices have limited this capacity. For example, the UK has 2.8 doctors for every 1000 people compared to an average of three in OECD countries generally and more than four in Germany, Italy or Switzerland. We have only 2.46 hospital beds per 1000 people, compared to 8.0 in Germany or 5.9 in France. And we have fewer intensive care spaces than the average developed economy.

The NHS is under pressure because of past political decisions to limit its capacity. Failing to point this out exonerates what should not be exonerated - namely, a decade of fiscal austerity.

What's happening here is, in fact, a widespread error - of regarding something as exogenous or given when it is in fact a creation of people, either deliberately via policy or inadvertently via emergent processes.

Another example of this mistake lies in the debate over how far Labour should accommodate itself to social conservatism. What some of this misses is that whilst there have always been social conservatives, they have not always been so salient or an insuperable obstacle to progress. Instead, the strength of social conservatism today is a product of economic conditions. As Ben Friedman has shown, stagnation breeds illiberalism. And Kenan Malik adds that, among working class voters, it is also "the product of decades of neglect."

The strength of social conservatism is partly endogenous. One trivial fact tells us this. It's that before 2016 hardly any of us were "leavers" or "remainers"; these are identities that were created by political debate.

There's more to politics than merely giving punters what they say they want. As Kenan says, it is also "about standing on a set of principles and trying to win people over" - or, I would add, shifting the agenda from the culture wars to economics.

Social conservatism, though, isn't the only example of public opinion being (partly) endogenous. Kris-Stella Trump has shown that the same is true of our attitudes to fairness. When inequality is high we regard that as fair, and when it is low we also see that as fair. Our perceptions of fairness are anchored by (what we perceive to be) the actual distribution of income.

Even the most intelligent social observers can sometimes fail to distinguish between the exogenous and endogenous. I'm thinking here of two otherwise excellent recent books, Case and Deaton's Deaths of Despair and Thomas Phillipon's The Great Reversal. Both show how capitalists have captured the state in order to extend their monopoly power. But their response to this is to advocate better policy, as if doing so were only a matter of intellect and goodwill.

Which it is not. Such proposals fail to see what they themselves have shown - that dysfunctional policy is endogenous, the product of capitalists' political power. The remedy for this is not for policy-makers to simply try harder. It is for us to work for a stronger anti-(crony?) capitalist movement, so that policies to restrain rent-seeking become more feasible.

There is, of course, another example of confusing the exogenous and endogenous and one that's been with us for decades. I'm thinking of the tendency to regard capitalism as natural, as the result of some innate human impulse to truck, barter and exchange. But this is not true. And believing that it is limits our ability to imagine a better world. As Ellen Meiksins Wood has written:

The naturalization of capitalism, which denies its specificity and the long and painful historical processes that brought it into being, limits our understanding of the past. At the same time, it restricts our hopes and expectations for the future, for if capitalism is the natural culmination of history then surmounting it is unimaginable. (The Origins of Capitalism, p8)

But capitalism is not natural. People have made it. And what we have made, we can change.