Imagine it as a bet with a friend. You: "hey, I got this item worth 10 but I believe it will go down in the next five days." Friend: "no way." "want to bet? You will buy it from me for 10 whenever I want to sell it." "nah." "I will give you 2 to keep right now!" "alright."

Your friend has no say when or if you sell. He got paid and hopes you are wrong. Your friend will obviously not agree to pay 10 for an item that is already only worth 5. And yes if the item only goes down to 9 you lost 1 on the bet.