So like in tennis, usually it's win-lose; it always adds up to zero-zero-sum. But if you're playing doubles, the person on your side of the net, they're in the same boat as you, so you're playing a non-zero-sum game with them.
Deci ca in tenis, de obicei avem castig-pierdere, intotdeuna se insumeaza in mod nul, dar daca joci la dublu, persoana de aceeasi parte a fileului este in aceeasi barca cu tine, deci jucati cu ea un joc cu suma ne-nula.