Let your plans be dark and impenetrable as night, and when you move,
fall like a thunderbolt.
The original text has 震 instead of 霆. Cf. IV. § 7. Tu Yu quotes a
saying of T‘ai Kung which has passed into a proverb:
疾雷不及掩耳疾電不及瞑目 “You cannot shut your ears to the thunder or
your eyes to the lightning—so rapid are they.” Likewise, an attack
should be made so quickly that it cannot be parried.