The zero-sum nature of many markets is arguably the most important concept in markets. Larry Harris, chair in finance at the Marshall School of Business at
University of Southern California: “Trading is a zero-sum game when gains and losses are measured relative to the market average. In a zero-sum game, someone can win only if somebody else loses.

Three groups of stylized characteristic traders are examined.
Winning traders trade for profit.
Utilitarian traders trade because their external benefits of trading are greater than their losses.
Futile traders expect to profit but for a variety of reasons their expectation are not realized.

Winning traders make prices efficient and provide most liquidity.
Utilitarian and futile traders effectively underwrite the winning traders’ efforts.

Our study will examine many different trading styles. Trading styles generally are
associated with specific types of traders. We shall consider the styles of value-motivated traders,
inside informed traders, headline traders, event study traders, dealers, market-makers, specialists,
scalpers, day traders, upstairs position traders, block facilitators, market data monitors, electronic
proprietary traders, quote-matchers, front-runners, technical traders, chartists, momentum traders,
contrarians, pure arbitrageurs, statistical arbitrageurs, pairs traders, risk arbitrageurs, bluffers,
"pure" traders, noise traders, hedgers, uninformed investors, indexers, pseudo-informed traders,
fledglings and gamblers.

Very enlightening paper. It´s interesting how the author categorizes the traders by type and evaluates their strategies in order to define whether they are losing or winning.
There are many traders who ignore this thinking or refuse to believe it but in my opinion the zero-sum game is important concept in markets.