Use your example to illustrate. Party A's long position 100 yuan/lot, and Party B's short position 100 yuan/lot. Subsequently, Party A sold it to Party C at the price of 90 yuan/hand. At this point, Party A lost 10 yuan/hand, which has nothing to do with future transactions.
On the last trading day, Party B and Party C did not close their positions, but delivered them in cash. At this point, the delivery price is determined by the spot price. If the spot price at this time is 95 yuan/hand, and both Party B and Party C make money from 5 yuan/hand, then the money earned by the two 5 yuan/hands is 10 yuan/hand (excluding commission and other expenses). If the spot price at this time is 80 yuan/hand, then only B earns 20 yuan/hand, and what he earns is 10 yuan/hand, which is lost by A and C respectively; On the other hand, if the spot price at this time is 1 10 yuan/hand, then only C makes money in 20 yuan/hand, and he earns 10 yuan/hand where A and B lose money respectively. If the spot price is 90 yuan/hand, B earns 10 yuan/hand, that is to say, A loses 10 yuan/hand, and C does not lose or earn; If the spot price is 100 yuan/lot, and Party C makes 10 yuan/lot, that is, Party A loses 10 yuan/lot, and Party B does not lose or earn.
Do you understand the relationship between making money and losing money? Therefore, the secondary markets such as stock market and futures are all zero-sum games. There is a loss, there is a gain.
If you think it is satisfactory, please adopt it. Thank you.