The person you borrow from gets a small guaranteed win because you get paid a small amount for the privilege of borrowing their shares. The one who loses is whoever bought the shares at the higher price. That can be the person borrowing the shares, or it can be another person interacting with the stock market at the other end of your transaction.
When shorting stocks, a stock is borrowed, and then sold. Whoever they borrowed the stock from is the loser here
The person you borrow from gets a small guaranteed win because you get paid a small amount for the privilege of borrowing their shares. The one who loses is whoever bought the shares at the higher price. That can be the person borrowing the shares, or it can be another person interacting with the stock market at the other end of your transaction.