You can be sure of succeeding in your attacks if you only attack places which are undefended. [Wang Hsi explains "undefended places" as "weak points; that is to say, where the general is lacking in capacity, or the soldiers in spirit; where the walls are not strong enough, or the precautions not strict enough; where relief comes too late, or provisions are too scanty, or the defenders are variance amongst themselves."] You can ensure the safety of your defense if you only hold positions that cannot be attacked.
