“Most economic fallacies derive from the tendency to assume that there is a fixed pie, that one party can gain only at the expense of another.” -Milton Friedman

I just googled "Fixed pie fallacy" - I was assuming (probably wrongly) that most people were familiar with it. I'm not even certain Friedman was the first to identify it.

The first thing I come up with on Google is [1]. It's a decent overview.

[1] http://mjperry.blogspot.com/2006/12/fixed-pie-fallacy.html