A zero sum game is one in where if you win, I lose, and if I win, you lose. It's competition instead of collaboration, and unfortunately competitive sports often drive this mentality into us that this is the way the world works, when in reality if you want to win big in this life, you need to collaborate more than compete.
Competing is all relative, it's all about measuring yourself against the other guy. This can be helpful in some cases, like benchmarking, so that you know what's possible and you can improve yourself or your business, but it's harmful when it becomes ALL about catching up with the competition and staying ahead, especially when you are willing to damage your competition so that you can "get ahead" of them by pushing them behind. That means they're behind, but it doesn't mean you're making any progress, or that you're better off.
The opposite of a zero sum mentality is win-win. It's looking for "How can we both come out ahead by working together?" rather than assuming that if the other guy wins, you must be losing.
