@coolboymew @lottev
>You buy stocks now and agree to pay later, which then your profit happens if the stock falls
You got that a bit wrong I think. You sell stock now (that you don't have) for $10, and agree to give the stock to the new owner next week. Until then you expect the stock to drop to $5, so you yourself buy it later on for that $5 and immediately give it to the guy who bought it from you last week. Result: $5 profit.
But if instead of the stock dropping, it increases to $20, you're forced to buy at that price, and give it away to the guy who bought from you last week with $10. Result: $10 loss.