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.
It is sufficient to estimate the enemy situation correctly and to concentrate your strength to capture him. There is no more to it than this. He who lacks foresight and underestimates his enemy will surely be captured by him.
Why wilt thou be so sottish, such an enemy to thyself, as to prefer puddle-water, and that poisoned too and stolen, before pure living waters out of thy own well?
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.