Every game has to be a sort of conflict in a positive way. Maybe if you do not have some kind of conflict with your partner, you'll never know what he think or what he will do.
A game can become a quarrel and it is very good for the rivals if that it can be a sharp battle, but sometimes the rivals start to fight for real.
How the game can become the war?
If partners are not fair players, they can get angry. If you are the fair player, you'll never become troublesome, you can only become sad for awhile.