Document toele:
The Winners and Losers of the Zero- Sum Game: The Origins of Trading Profits, Price Efficiency and Market Liquidity

Summary:
Trading is a zero- sum game when measured relative to underlying fundamental values. No trader can profit without another trader losing. People trade because they obtain external benefits from trading. These benefits include expected returns from holding securities, risk reduction from holding correlated assets and gambling entertainment

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• The Winners and Losers of the Zero-Sum Game