Any game in which a number of players must play for portions of a fixed amount of material, i.e. chips, money, xp, energy, etc. The meaning of this is that whenever one player increases their score, the score of the rest of the group must decrease by the same amount. Poker is the best example of a zero sum game. Blackjack and other house games are also zero-sum games, but for all practical purposes they are not, as you will be thrown out of the casino long before the house lets you make any significant dent in their cage.

A common logical fallacy is to compare a complex issue in economics to a zero-sum game. This is most frequent when you hear about how, say, the United States has one quarter the population of India, yet consumes three times the world's resources. This may be indicative of an inequality, but the statement erroneously implies that if we Americans were to limit our consumption, this would somehow encourage the GDP of India to rise. In all likelihood, the opposite would be true, as the decrease in consumption would include a decrease in consumption of Indian goods, which would depress the nation even more. Another reason this argument is bad is because some of the goods consumed are not static resources, such as grain, which (these days) is grown according to demand.

You may also find that some noders complain about how other people's writeups get voted on and cooled more than theirs, as though voting was a zero-sum game. Although there is indeed a limited number of votes available per day, this is fallacious because it implies that all votes are used every day, and that if other nodes didn't get voted on, their nodes would get voted up.

Most elements of the economy are not zero-sum games. Some are.

At any given time, the amount of arable land on the surface of the earth is limited. This amount can vary naturally, or it can be increased technologically (or decreased through human mismanagement). Land is a cornerstone to any economy, be it hunting and gathering, pastoral or sedentary agriculture, or industry. And hey, surprise surprise, but conquest is the single most common reason for war throughout history. Why? Because the acquisition of land is a zero-sum game.

At any given time, the number of marriageable females and marriageable males is limited. These amounts can vary naturally, or can be decreased through human violence. In particular, as for all zero-sum games, if you decrease the number of competitors, you increase your spoils (wives or husbands). Since males are physically stronger than females, it is most likely males who are going to be doing the feuding, which means that we could predict polygamy to be more common than polyandry, and that it would be most common among violent, affluent societies or the affluent segments of violent societies.* Oh wow look, it's true! I'll be darned.

Also, in many contexts, because producing something for yourself are far more expensive than simply taking it by violence, the economy might as well be zero-sum.** For example:–

Let's say you're a Goth. The Goths were cow-herders. They were also warriors, because others would try to take their cows in times of hardship, and sometimes they would have to take other peoples' cows.

Now, let's say I'm a Roman. We're pretty soft, and we have wealth you could never produce in ten lifetimes.

You have two options: Try to assimilate into Roman culture, where you will invariably be at the bottom because of your relative poverty; or try to take what you can by force, which will most likely be everything.

So what's the reasonable thing for you to do?

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* Some people solve the zero-sum problem of mating by simply having monogamy. This works fine under all but the most bizarre of natural circumstances, since the natural ratio of males:females is so close to 1 that the variation is usually negligible. On the other hand, some people, like the Yanomamö, lock themselves into a cycle of perpetual warfare by artificially (and accidentally) creating a very violent zero-sum game. One's status is determined, in part, by the number of wives one owns, and the number of men one has killed. Therefore, the Yanomamö will go out on raids with their buddies, kill the men of other villages and take their wives and daughters away as wives of their own. Of course, in order to have larger raiding parties, the Yanomamö privilege male children, even to the point of committing infanticide on females or leaving them to starve, so that they will have a larger and healthier male army. This reduces the supply of females, increasing the demand....

** Capitalism increases the benefit of assimilating into a culture because of the relative free-flow of wealth, making it possible to end poverty conditions far easier than in, say, feudalism. Gunpowder decreases the potential spoils you could get from raiding (or taxing, theoretically). When used properly, they are the twin cornerstones of peace.

A zero sum game is one in which the total amount of 'points' remains constant. One player's loss is the other player's gain. Payments are made only to the other players.

The simplest of zero sum games is the classic matching coins game.

• Two players agree to one being "even" and the other being "odd".
• Each player shows a penny.
  • Pennies are shown simultaneously
  • Each player may show a head or a tail.
• If both show the same side, then "even" wins the penny from "odd".
• If each shows a different side, then "odd" wins the penny from "even".

Or, the payoff for the game.

         ._______odd______.
         |  Head  |  Tail |
Even Head|  1,-1  |  -1,1 |
     Tail|  -1,1  |  1,-1 |

Adding up the payoffs in each cell, the sum of them is 0, hence, a zero sum game.

Formally this is defined as: If all the wins and losses in a game are totaled, treating losses as negatives, the sum for each set of strategies chosen is 0.

Or, less formally, a zero sum game is one in which one player's winnings equal the other player's losses.

You might imagine adding up all the universe's resources: labor, land, raw materials, equipment, technology, knowledge, etc... into a pie. At different times, different people may have control of different percentages of this pie, but the size of the pie isn't constant. Improvements in technology can get you access to other planets, more solar radiation, deeper into the ocean or earth's crust, more efficient use of existing resources - thus increasing the size of the pie. If the size of the pie can be increased, then of course other actions can also decrease it.

This isn't to say nothing should ever be done about the relative amounts of the pie that different people control. Obviously the more parts of the pie allocated to serving a smaller percentage of the population, the less that will be available for everybody else. However, it is both a fallacy to say that society can only be improved by improving the pie's distribution, and a fallacy to say that society should only be improved by increasing the size of the pie.

Resource allocation is very important to the survival of society. If I spend all my time, food, and energy building a bridge that many people will use, while someone else spends all his time and energy building a bomber and explosives to take out the bridge, then in the end, the resources allocated toward both our activities were pretty much wasted.

On a less extreme scale, if I use up a lot of resources to build a bridge that nobody wants to use, then my personal efforts were wasted.

The spectrum continues: if I spend a lot of resources in trying to convince others to buy a product they didn't originally want (advertising), and keep doing it until I finally convince them to want it, and then spend more resources to produce the things they've been convinced to want, that too isn't exactly an efficient use of resources.