Short Selling Has Unlimited Downside and a Clock Attached
Selling something you do not own inverts the payoff of ordinary investing. Losses are theoretically unbounded, costs accrue daily, and being right too early is the same as being wrong.
The Mechanics
A short seller borrows shares, sells them, and later buys them back to return. If the price fell in between, the difference is profit.
The payoff is the inverse of a long position and it is not symmetric.
| Long position | Short position | |
|---|---|---|
| Maximum gain | Unlimited | 100 percent, if it goes to zero |
| Maximum loss | 100 percent | Unlimited |
| Position size as it works | Grows | Shrinks |
| Position size as it fails | Shrinks | Grows |
A short position gets larger as it goes against you and smaller as it works. That is the opposite of every other position and it is why position sizing matters more here than anywhere else.
The Running Costs
Time is not neutral. Three costs accrue while the position is held.
Borrow fees, paid to whoever lent the shares, which can be substantial on heavily shorted names.
Dividends, which the short seller must pay to the lender, since the lender is entitled to them.
Margin financing, since short positions require margin and the collateral has a cost.
Against these, the short seller earns interest on the sale proceeds, which mattered little when rates were near zero and matters considerably more when they are not.
Why Being Early Is Fatal
A long investor with a correct thesis and bad timing waits. The position may decline and it does not force any action, and the eventual outcome is the same.
A short seller with a correct thesis and bad timing faces a growing position, accumulating costs, and rising margin requirements. They may be forced to close before the thesis plays out.
Many of the most celebrated short theses in history were correct and cost their holders money, because the position could not be maintained long enough. This is the practical meaning of the observation that markets can remain irrational longer than a leveraged participant can remain solvent.
The Squeeze
Rising prices force covering, which raises prices further. Two structural features make this worse.
High short interest relative to available shares means many participants must buy from a limited supply. And recall by lenders forces closures at the worst possible moment.
The 2021 episodes in heavily shorted retail stocks demonstrated the extreme version, where concentrated short interest, options hedging flows, and coordinated buying combined into moves that bore no relation to the underlying businesses.
Naked Shorting and Settlement
Selling short without having borrowed or located shares is naked short selling, prohibited in most developed markets.
The concern is that it permits selling more shares than exist, and it produces settlement failures where the buyer does not receive what they paid for. Regulations require locating shares before selling and impose close out obligations on persistent failures.
What Shorts Contribute
Short sellers are unpopular and they perform a function. They are the participants with a financial incentive to investigate whether a company is misrepresenting itself.
Several major frauds were identified publicly by short sellers before regulators or auditors acted. The research was funded by the prospect of profiting from the decline, which is precisely the incentive that made the work worth doing.
Short selling bans, introduced during several crises, have generally been found to worsen liquidity and widen spreads without supporting prices durably.
The Bottom Line
Short selling caps the gain at 100 percent and leaves the loss unbounded, with the position growing as it moves against you. Borrow fees, dividends, and financing accrue daily, so being right late is the same as being wrong. The function shorts perform in identifying misrepresentation is real, which is why bans on them have generally made markets worse rather than better.