出其不意

Explanation: It: pronoun, the other party; unexpectedly: did not expect. While the other did not expect to take action. 　　Usage: -Linked; as predicate, object, attribute; that people do not prepare a sudden action by 　　Source: Sun Tzu "Sun Tzu Posts count": "Attack is unprepared, surprise." 　　Examples: Today is years late, the old must be at home, surrounded by troop movements at this time, ~, no side lost. (Mingling 濛 beginning "of half an hour Pai An Jing Qi" IV) Thesaurus:  take sb. unawares, to help a joint cause Wish watch, Surprise, The enemy is unprepared, Ji lei Less Their ears, sudden; as sudden as lightening; sudden peal of thunder leaves no time for covering ears