Another simple way to look at this is to reverse the farming/buying and selling model. Players start the game with 0 gil. They farm something and sell it on the MB until they have some gil. Then, they buy low and sell high to gain a profit off items. This approach REQUIRES you to have gil now, BEFORE you can make a profit. Short selling is the reverse of this as you don't need any gil to start. A brand new player with 0 gil can immediately borrow an item and use short selling as a means to make gil without farming and selling. This approach requires NO GIL to yield a profit. (I know, you don't immediately have MB access with a brand new character, this is to demonstrate a point.)