Never abandon the possibility of attack. Attack even from a position of inferiority, to disrupt the enemy's plans. This often results in improving one's own position.
You may have enemies whom you hate, but not enemies whom you despise. You must be proud of your enemy: then the success of your enemy shall be your success too.
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.
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.