It isn't a zero sum game. Wealth is created, things like new farmland in the Netherlands, buildings that last more than one lifetime and the like. As a result people today are in some sense far wealthier than they were in the past. In developed societies virtually everyone has indoor plumbing and climate controlled living conditions, things that didn't used to be available to even the fabulously wealthy.
But it has some similarities to a zero sum game since total wealth changes slowly, and large short term gains by one group mean taking it away from another. The real problem is that it is really, really complex. And our understanding of economics might be compared to Faraday's understanding of electromagnetic theory. We have some strong empirical relationships, but no theory of everything.
This complexity and ignorance is made clear with the example of woman joining the work force. A simplistic view is that income (and perceived wealth) will double. But various factors (like the hidden cost of child care, housework and food preparation that wasn't acknowledged when woman only worked in the home, and the real but maybe not admitted costs of working like clothing and another car) make that change far, far smaller. Add new necessities like cell phones, computers and the like along with health care and education costs rising at rates far higher than general inflation and the whole benefit just evaporates.