Let’s call it a game, any thing you and I do together.
A zero-sum game is a thing we do where, for you to win, I have to lose. A situation (competition? negotiation?) with finite resources. If I get more, you get less. We share one cake. If my piece is bigger, your piece gets smaller.
We often think of things as zero-sum games when they can really be positive-sum games, games where nobody needs to lose, where all parties can come out ahead.
Teaching is wonderfully positive-sum. I can give knowledge to you without losing it myself. Maybe you teach me something, too. Either way, our net knowledge is more than we started with. Good game.