But what if the sought-after thing was $100 itself?
What if people produced goods to obtain money, not merely as a transactional device to be swiftly exchanged for other things, but as a store of value, to be held indefinitely?
A widespread propensity to hoard money posed a problem for Say's vision.
It interrupted the exchange of goods for goods on which his theory relied.
Unlike the purchase of newly created products, the accumulation of money provides no stimulus to production (except perhaps the mining of precious metals under a gold or silver standard).
And if, as he had argued, an oversupply of some commodities is offset by an undersupply of others, then by the same logic, an undersupply of money might indeed entail an oversupply of everything else.
Say recognised this as a theoretical danger, but not a practical one.
He did not believe that anyone would hold money for long.
Say's own father had been bankrupted by the collapse of assignats, paper money issued after the French Revolution.
Far from hoarding this depreciating asset, people were in such a rush to spend it, that “one might have supposed it burnt the fingers it passed through.”
In principle, if people want to hold more money, a simple solution suggests itself: print more.
In today's world, unlike Say's, central banks can create more money (or ease the terms on which it is obtainable) at their own discretion.
This should allow them to accommodate the desire to hoard money, while leaving enough left over to buy whatever goods and services the economy is capable of producing.
But in practice, even this solution appears to have limits, judging by the disappointing results of monetary expansions since the financial crisis of 2007-08.
Today, many people scoff at Say's law even before they have fully appreciated it.
That is a pity.
He was wrong to say that economy-wide shortfalls of demand do not happen.
But he was right to suggest that they should not happen.
Contrary to popular belief, they serve no salutary economic purpose.
There is instead something perverse about an economy impoverished by lack of spending.
It is like a subsistence farmer leaving his field untilled and his belly unfilled, farming less than he'd like even as he eats less than he'd choose.
When Say's law fails to hold, workers lack jobs because firms lack customers, and firms lack customers because workers lack jobs.
Say himself faced both a ruinous shortage of demand for his cotton and excess demand for his treatise.
The first edition sold out quickly; Napoleon blocked the publication of a second.
Eventually, Say was able to adapt, remixing his activities as his own theory would prescribe.
He quit his cotton mill in 1812, notes Mr Schoorl.
And within weeks of Napoleon's exile in 1814, he printed a second edition of his treatise (there would be six in all).
In 1820 he began work once again at the Conservatory in Paris—not this time as a student of spinning, but as France's first professor of economics, instructing students in the production, distribution and consumption of wealth.
He considered it a “new and beautiful science”.
And, in his hands, it was.