Short selling, a common financial transaction behavior.
Bupen's stock brokers use the simple, intuitive method of "buying sizes" to explain to clueless customers what long and short mean—such a straightforward explanation makes it easier for customers to understand what they're facing.
More specifically, the price of a financial product is one hundred dollars each; at this point, A borrows one item from B and sells it to other buyers, so A has a hundred dollars.
After some time, when the product drops to fifty dollars each, A spends fifty to buy back a product and returns it to B.
In this transaction, A profits fifty dollars from the price difference due to the product's drop, which is the process of profiting from short selling.
If the product doesn't drop but instead rises, you lose as much as it rises.
