The art of war teaches us to rely not on the likelihood of the enemy's not coming, but on our own readiness to receive him; not on the chance of his not attacking, but rather on the fact that we have made our position unassailable.
故用兵之法，無恃其不來，恃吾有以待之；無恃其不攻，恃吾有所不可攻也。
Original text (Chinese)