I never stop. There's always something to discuss. When someone agrees with me too quickly, that's when I switch sides and find things that support the other point of view. It's useless to discuss something when not all arguments are used. It's not even necessary for the other person to change his mind. Believing that you have to achieve something like that is bad. We're all narrow-minded in our own simplistic way, the only thing you can do is keep discussing things to find out how many different views there are. It doesn't matter how tough you make the debate. Even just shouting insults at eachother is often eye-opening. In the heat of the discussion stupid things may be shouted, but sometimes very true things as well.