It's a zero sum game with extra steps. The "sum" varies over time. If both players come out ahead, then one always pays an opportunity cost equal to the amount

It's a zero sum game with extra steps. The "sum" varies over time. If both players come out ahead, then one always pays an opportunity cost equal to the amount they would've gained had they stayed in the market longer. In other words, it's win/lose, not win/win once you extend the timeline and compare what it would look like had the trade not had happened.