[alex_young]

> If person A borrows a stock from person B then sells it to person C, they can borrow the stock back from person C and sell it again. No naked short involved.

Naive question: Why would that ever happen? Wouldn't this scenario just cost person C commissions with no opportunity for gain?

[kcg]

In this scenario, Person C still owns the stock and will gain/lose with the stock's rise/fall. Person A borrowing from C at the end is just borrowing, not buying. At some point Person A needs to return stock to Person C.

[alex_young]

So in this example person A could keep selling the same share over and over again? How would the multiple “owners” realize their gains if they all decided to sell on the same day?

[kcg]

Person A can only sell the number of shares they've borrowed. If Person A borrows a share from Person C, they can sell that one share only. To sell more without borrowing additional shares would be naked shorting, which is prohibited.

You might be asking instead about the following scenario, though, where a single share is borrowed and sold short multiple times:

Person A borrows from Person C and sells to Person B

Person D borrows from Person B and sells it to Person E

Well, the covering of the shorts doesn't have to happen in an atomic transaction; there are thousands to millions of trades of a single ticker every day. Just as a single share can create a chain of multiple shorts (borrows and sales), a single share can cover multiple shorts too through a chain of trades.