Zero-sum games are games where the amount of "winnable goods" (or resources in our terminology) is fixed. Whatever is gained by one actor, is therefore lost by the other actor: the sum of gained (positive) and lost (negative) is zero.Conservatives rightly criticize liberals for viewing the economy and educational attainment as zero-sum games; liberals rightly criticize conservatives for thinking the same about individual liberty. A classic example of a false zero-sum-game is the task of dividing a cake among people when it is possible to bake another cake.
For example, the conflict between gay rights and the rights of religious organizations is commonly characterized as a zero-sum game, when there is no good reason why it should be. Religious people should be free to do what they like among consenting adults in the privacy of their own churches, on their own dime, and with no special privileges to protect them from competition from other churches that see things differently. Churches should be free to exclude LGBT people, but the people excluded should be free to start their own churches or other organizations and compete on a level playing field; it worked for Troy Perry. On the issue of whether churches should recognize same-sex marriage, both the Catholic Church and the Universal Fellowship of Metropolitan Community Churches should get to set their own rules, and secular government should show no favor to either. In short, bake another cake.