A zero sum game is a term used in game theory to describe both real games, and situations of all kinds, usually between two players or participants, where the gain of one player is offset by the loss of another player, equaling the sum of zero. For instance, if you play a single game of chess with someone, one person will lose and one person will win. The win (+1) added to the loss (-1) equals zero.

Games where there can be multiple winners are called non zero sum and they are becoming less common and less applicable in modern life. To be a true zero sum game, losses of one party have to be exactly equal to gains of another party. Since sometimes a loss can be a gain, real life examples of the zero sum game are more difficult to find.

If you play chess in a tournament, each individual match is zero sum, with one winner and one loser. However, outside of the game, you are given a number ranking. This ranking can change significantly if you lose to someone of a much lower rank. It may not alter much if you lose to a much higher-ranking player. When a single game is actually one in a series with an outside ranking, the total result may be non zero sum, since wins or losses are not the only thing that count.

It could also be suggested that the zero sum game is an extremely simplified manner of looking at something like chess, which is not a probability-based game. A loser may gain as much from his losses as he does from his wins. He may become a better player as a result of losing; so though technically the game comes down to one winner and one loser, it may be advantageous to lose. Players matched against those with much greater skill may be more interested in learning than winning.

A couple's argument may perhaps be a zero sum game but it depends on the maturity of the couple. While it might be thought that there has to be one winner and one loser, this is not always the case. If Mr. and Mrs. Smith are arguing about who will drive to the store, Mrs. Smith might give in and allow Mr. Smith to drive. Hence the driver is +1 and the non-driver is -1. Suppose a compromise is reached where Mr. Smith drives to the store and Mrs. Smith drives back. Still each party to the argument has a gain equal to the loss. The result is + one-half, -one-half, resulting in a zero sum.

Yet if arguments are frequent, analysis of winning or losing in a single match may be far less important than analysis of the total marriage. Both couples may be losers by the argument if it creates mutual bad feelings. The sum can quickly sink below zero if two people are constantly at each other’s throats.

The term zero sum game may also be extrapolated to economics and the trading practices between two countries. Equal trade is essentially a zero sum game. Both countries gain equal advantage by acquiring something and by giving something up. Lots of trade situations are non zero sum. One country loses more than it gains in making a trade. Again, this applies to the overall picture. Perhaps the country that trades at a disadvantage gains something non-tangible, like the respect of another nation and better diplomatic relations. As in chess where the loser may profit by his loss, a nation that takes an economic loss in a trading situation may profit in other ways.

In diplomatic relations, there can be win-win, instead of win-lose situations. People or countries may equally benefit without losing. Usually, however diplomacy comes down to compromise, both parties giving up something to gain something. When the things given up are fairly equal to the things gained, this is still a zero sum game. Negotiation and diplomacy are often called “spreading the pain evenly.”