In 1829 the then-young economist John Stuart Mill put his finger on how it was that there could be excess supply of everything in the economy – of pretty much all currently produced goods and services and all kinds of workers. Previous economists had asserted a “metaphysical necessity” that excess supply of one commodity be matched by excess demand for another: that if there were unemployed cobblers then there were desperate consumers frantically looking for more seamstresses, and thus the economy's problems were never those of a general shortage of demand but of structural adjustment. These thinkers, Mill was the first to point out, had forgotten about the financial sector. If there was an excess demand for financial assets, then there could be an excess supply of everything else – what we call a depression.
1829年，當時還很年輕的經濟學家約翰•斯圖亞特•穆勒(John Stuart Mill)指出了經濟中過度供應（包括目前生產的所有商品和服務以及各種類型的工人）是怎麼一回事。以前的經濟學家主張一種「形而上的必然性」，即如果一種商品過度供應，就必然存在對另一種商品的過度需求：如果有鞋匠失業，那麼就會有顧客迫切需要更多的女裁縫，因此經濟的問題從來不是需求普遍短缺的問題，而是結構性調整問題。穆勒率先指出，這些學者沒有考慮金融業。如果對金融資產存在過度需求，那麼就可能存在其它所有商品過度供應的情形——我們稱之爲蕭條。