The story goes that in 1928 or 1929, Joseph Kennedy, speculator and future patriarch, sat down for a shoeshine and the boy working on his shoes gave him stock tips. Kennedy is said to have gone back to his office and started selling everything, reasoning that when the shoeshine boy has tips, there is nobody left to buy. Flag it honestly: this is legend, told and retold in many versions, and no one can verify the shoeshine chair. It survives, like Newton's quote from the South Sea year, because it names something true. A market rises on new buyers. When stock tips have reached the last person in the economy who was not yet in, the market has run out of fuel, and 1929's fuel was more combustible than anyone wanted to believe.
What people believed
The late 1920s in America felt, from inside, like the future arriving on schedule. Electricity, automobiles, radio, mass production: real technologies, really transforming life. Out of that truth grew the belief that does the damage in every era, the conviction that this time the old rules are repealed. Commentators spoke of a new era of permanent prosperity. Days before the crash, Irving Fisher, one of the most respected economists alive, famously declared that stocks had reached what looked like a permanently high plateau. He was not a fool. He was a brilliant man inside a belief.
And the belief had a retail version: stocks only go up, so owning them is not speculation but common sense, an escalator anyone could step on. Ordinary people who had never owned a share opened brokerage accounts. J.K. Galbraith, whose short and lethally funny book The Great Crash 1929 is the essential account of all this, is careful on one point: fewer Americans actually owned stocks than the legend suggests. But the market had become the national conversation, and the people who were in were in deep, because of the machine described next.
How it inflated: margin, the rocket fuel
You could buy stocks in the 1920s "on margin," and this is the single concept that explains both the boom and the catastrophe, so take it slowly.
Buying on margin means buying with borrowed money: you put down a fraction of the price in cash, your broker lends you the rest, and the shares themselves serve as collateral, the thing the lender can seize if you fail to pay. In the late 1920s, by many accounts, that fraction could be as little as 10%. The loan is not patient money. If the shares fall enough that the broker doubts the collateral covers the loan, the broker demands you add cash immediately. That demand is a margin call, and if you cannot meet it, the broker sells your shares, at whatever the market pays, whether you like it or not.
Now the arithmetic, in modern euros to keep it familiar. You have €1,000.
| Scenario | Cash buyer (€1,000 of stock) | Margin buyer (€1,000 down, €10,000 of stock, €9,000 owed) |
|---|---|---|
| Stock rises 10% | €1,100. You made €100. | Stock worth €11,000, minus €9,000 owed: €2,000. You doubled your money. |
| Stock falls 10% | €900. You lost €100, on paper, and can wait. | Stock worth €9,000, minus €9,000 owed: €0. You are wiped out, and sold out. |
On the way up, margin multiplied every gain roughly tenfold, and those gains recruited the next wave of buyers, whose buying pushed prices up, which created more gains, which recruited more buyers. Brokers' loans grew to enormous size; Galbraith records that lending money to margin buyers became one of the most profitable businesses in the country, drawing in cash from corporations and banks alike. And the era found a way to stack leverage on leverage (leverage is the finance word for amplifying a position with borrowed money, exactly what margin does): investment trusts, companies whose only business was owning shares of other companies, often themselves bought on borrowed money, sometimes holding shares of other trusts. Galbraith's chapters on the trusts read like satire, except every prospectus was real. By 1929 a single dollar of underlying business earnings could have several layers of paper claims balanced on top of it, every layer assuming prices would hold.
The same wire that pulled everything up ran in reverse. That is not a metaphor. It is the same wire.
Leverage converts a temporary fall into a permanent loss, because it takes away the one thing a falling market cannot otherwise take from you: the choice not to sell.
How it burst
Prices wobbled through September and October 1929. Then, on Thursday, October 24, Black Thursday, the wobble became a rush for the exits. So many sell orders hit the market that the ticker, the machine printing prices, ran hours behind, which meant nobody could tell what their shares were worth, which is its own kind of panic. At midday a group of the most powerful bankers in New York pooled money to steady the market, and their representative walked the exchange floor placing showy bids. Galbraith recounts how the gesture worked for about two days.
On Monday the fall resumed, and Tuesday, October 29, Black Tuesday, was the worst day in the market's history to that point. Understand the mechanism, because it is the margin arithmetic running backward with nobody's hand on the wheel. Prices dip. Brokers, watching collateral shrink, send margin calls. Buyers who cannot add cash are sold out by force, at market. That forced selling pushes prices lower, which triggers the next layer of margin calls, which forces more selling. The investment trusts, leveraged holders of leveraged holdings, amplified every step down as faithfully as they had amplified every step up. No villain is required, no conspiracy, no single decision. A doom loop is just leverage plus a price dip, and it feeds on itself with mechanical patience until the leverage is gone.
And here is the part the movies compress: October was only the beginning. The market rallied, sagged, and then slid, month after month, for nearly three years. By the summer of 1932 the major index had lost roughly nine tenths of its peak value. The crash bled into the Great Depression: banks failed, credit froze, unemployment reached catastrophic levels. Galbraith is careful, and we should be too: the crash did not single-handedly cause the Depression, but it shattered the credit and confidence of a fragile economy, and it turned a speculative cleansing into a decade of misery. That larger story deserves its own books. Ours stays with the investor.
The lesson
Earlier in this series, the compounding article drew a line between volatility and permanent loss: volatility is prices swinging while you still own the asset, and permanent loss is the swing becoming final because the asset is gone or you were forced to sell it at the bottom. 1929 is that distinction with the abstraction removed.
Consider two owners of the same shares in September 1929, shares of real, durable businesses. The first owns them outright with money she will not need for decades. The crash marks her holdings down brutally, on paper, and the paper stays ugly for years; by some measures the headline index took roughly a quarter of a century to regain its 1929 peak, though dividends along the way soften that picture. But nothing forces her hand. The businesses she owns go on making soap and soup and cigarettes through the whole Depression, and the strongest of them keep paying dividends. Her loss is real only if she chooses to make it real. Her risk was volatility, and volatility, for an owner who cannot be forced to sell, is weather.
The second owner holds the same shares with 10% down. The first serious dip does not merely mark him down; it takes his choice away. The margin call arrives, the shares are sold at the bottom by someone else's decision, and his participation in everything after, including the eventual recovery, is zero. Same businesses, same crash, opposite outcomes, and the entire difference is the borrowed money. The crash of 1929 did not destroy the patient, unleveraged owner of businesses. It destroyed everyone who had to sell, and leverage is the machine that manufactures people who have to sell.
If this era pulls you in, read Galbraith's The Great Crash 1929. It is short, it is funny in a way history books have no right to be, and it will inoculate you better than any warning label, because you will recognize the furniture of every future mania in it.
Do this now
Audit yourself for forced-seller risk. List every way you could be made to sell investments at a time not of your choosing: money invested that you will actually need within the next few years, any borrowing secured against your portfolio, the absence of a cash buffer for emergencies. You are looking for the wire that connects a falling market to your own hand. Find one such wire this week and cut it.
Next in the series: Manias IV: the dot-com crash, the mania recent enough to remember, in which the technology was real and the prices were not.