“A zero-sum assumption is that there is a fixed pool of any specific good and that in order for you to have more, someone else has to accept less. This is the essence of the common slogan, ‘there are only so many pieces of pie.’ If you want an extra slice, someone else has to accept one less. A positive-sum assumption, on the other hand, assumes that the pool of assets can be expanded. In other words, if there are not enough slices of pie for your liking, you can make a new pie for yourself. The important thing about zero-sum and positive-sum assumptions is that they form a mental pattern, an analysis program in our brains, coloring wide areas of thought.”
http://www.thedailybell.com/editorials/36225/Paul-Rosenberg-Production-Versus-Plunder–Part-2/