alt Hacker NewsDerivatives (options, futures, swaps, etc) are a zero sum market, there is always a winner and a loser necessarily because the contracts have an expiration date.
The same is not true for trading equities, they are not zero sum. There are dividends, buybacks, companies will sometimes spin off a part or parts as separate companies that you get newly issued shares of stock from (GE splitting into parts is a recent example), public companies get taken private at a premium to the market price, etc.
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The market has been heavily engineered and gamed to be positive sum. But sometimes I wonder could it turn out to be negative sum on certain timescales. That is that overall money would be lost on markets.
Presence of many options directly affect equity prices.
Futures are zero sum, but can also be a win for both sides, because what they gain is stability.
"I will buy y tons of corn from you in April for £x" - now I don't have to worry about how much my corn will cost and you don't have to worry about what your income will be.