To win, you make the rules.
Manzikert, Agincourt, Ireland; the Byzantines, French Norman Knights, and English Norman Knights expected the enemy to 'fight fairly', to 'fight by their rules', 'be Chivalrous', i.e. fight on terms/rules/laws determined by those who have the biggest advantage in their own system. Why would anyone fight like that? Why would you fight like that? What's the point? Allowing someone else to set the rules that you play by is nothing but a sure-fire way to lose at any given competition. If someone else has determined the rules/laws then it means that you are at an immediate disadvatage.
So how do you win? Make the rules, choose the rules that you will play by, fight by.
Choose rules that you want to fight by. Choose the battlefield in space and time that you will fight on. Choose the weapons that you and your opponent will fight with. Choose what the terms of victory are. Choose victory. Be victorious.
Dean Esmay found out that 'playing fair' 'being just' or 'playing by someone elses rules' doesn't work. He's right, most people aren't reasonable, they don't listen to reason, they listen to to physical force (e.g. a loud voice or imposing body lanugage) or appeals to some status symbol. As Dean says: 'being nice doesn't work'.