On Zero Sum Games (The Informational Meta-Game) (opens in new tab)

Different people value resources differently overall and also differently over time. Trading a resource you don't value as much to someone who does value it for something you value leads you both to be better off.

In a very simple form, if you're a fisherman you may have a surplus of fish, much more than you can eat before they go bad. Fish is not worth much to you, but maybe you need cloth for sails, the someone in the village collects and mends and sews cloth. They have a lot, but need food. Trading fish for cloth benefits you both.

Money is just an abstraction to smooth trades between people for resources they need. Scale to whatever level you want.

Trading is only zero-sum at very small time scales. Over longer times scales, the stock market is not a closed system. Traders who run out of money will either exit the market entirely, or find more money from somewhere else. That money comes from either economic profits, or the economy's money-creation process. In the US economy, that process is fractional reserve banking[0].

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[0]: https://en.wikipedia.org/wiki/Fractional-reserve_banking#Mon...

Apple the company issues stock. They are the seller, and some investor is the buyer. Apple uses the money to invest in operations, and the stock goes up over time. Who lost?

Forget about stocks - this is the whole point of trade in general. People have different resources and different needs, time horizons, risk tolerance etc., so the default assumption should be that voluntary trade is positive sum - just like Ford selling a car is positive sum even though there is a buyer and a seller.

Everyone can make or lose money depending on whether the value of the stock goes up or down and whether the participants own the stock or are borrowing it (short/negative ownership).

You mention two factors that can introduce new capital into the system, new investors and dividends, but seem to imply they are negligible or can be ignored... on the contrary those two factors are quite significant contributors and according to some theories dividends are the ultimate and total source of value in the stock market:

https://en.wikipedia.org/wiki/Dividend_discount_model

GTO means unexploitable. If the player were actually GTO, the worst case would be a draw. The novice playing a standard opening loses because he is a novice, not because he is playing GTO (he is not).