It is a zero sum game so that statement cannot be true unless you mean over time and in different places. If that is the case then it is a great argument for coming up with a set of rules beforehand that both parties agree is fair.
I agree with your comment; but I do have to point out the comment you're replying to specifically conceives a political landscape with more than two parties, that can indeed be considered as zero sum as well, yet two major parties can feasibly agree on something at a net loss for others.