Though fraud in all other actions be odious, yet in matters of war it is laudable and glorious, and he who overcomes his enemies by stratagem is as much to be praised as he who overcomes them by force.
Wars, therefore, are to be undertaken for this end, that we may live in peace, without being injured; but when we obtain the victory, we must preserve those enemies who behaved without cruelty or inhumanity during the war.
Our faith in others betrays that we would rather have faith in ourselves. Our longing for a friend is our betrayer. And often with our love we want merely to overcome envy. And often we attack and make ourselves enemies, to conceal that we are vulnerable.
So the principles of warfare are: Do not depend on the enemy not coming, but depend on our readiness against him. Do not depend on the enemy not attacking, but depend on our position that cannot be attacked.