What this is
Short selling is selling a security you do not own, in the expectation of buying it back later at a lower price. You borrow the shares from a holder (via your broker), sell them into the market, and later repurchase them to return to the lender. Profit is the difference — minus borrow costs and any dividends you must pay the lender while the position is open.
Why it matters
Shorts are the market's fraud detectors and its discipline on overpriced assets. The two most famous forensic short campaigns documented in this library — David Einhorn's Allied Capital thesis and his public Lehman Brothers analysis — show how a short is really a research product: the position is the output of evidence, not a mood.
How it works
Mechanics: locate shares to borrow → sell → post margin → repurchase (“cover”) → return shares. If the price rises, losses are theoretically unlimited — there is no ceiling on a stock price, and that asymmetry defines shorting.
Costs: borrow fees (which can spike on crowded shorts), dividends owed to the lender, and margin interest.
Squeezes: when many shorts must cover at once, forced buying drives the price up further — the dynamic behind the 2021 GameStop episode, which is also part of this library's indexed record of Michael Burry.
Forensic shorts: durable campaigns are built on accounting analysis — revenue recognition, capitalizing expenses, channel stuffing — documented point by point. That is why the best short theses read like research reports.
Example
Einhorn's Lehman thesis (2007–2008): a public, point-by-point argument that the bank's accounting for its real-estate exposures understated losses. Agree with every number or not, the structure is the lesson: claim → accounting evidence → observable outcome.
Common misunderstandings
“Short sellers crash companies.” Shorts cannot sell what other investors refuse to buy; they profit from detecting overvaluation or fraud that already exists.
“It's gambling.” It is a regulated, collateralized position — and the incentive structure behind much fraud detection.
“Unlimited downside” is often repeated but worth internalizing: a long can only go to zero; a short has no natural floor, which is why position sizing on shorts is a survival skill.
Key concepts
Borrow · locate · cover · squeeze · borrow fee · margin · forensic accounting · asymmetric payoff.