防不胜防

Explanation: Prevention: preparedness; win: do. Describe preparedness, however. 　　Usage: Contraction type; as the predicate attribute; that capacity is small, difficult to sustain 　　Source: Qing Wu Jian "Twenty years Strange": "This villain, really hard to detect." 　　Examples: A pair of children, there are the less fear, and indeed the most frightening duplicity of the so-called "comrades", as ~. (Lu Xun's "Letter To Yang Ji-yun") Thesaurus:  be taken by surprise, Down from the heavens, very unexpectedly, arise suddenly, dignity lose one's head Antonym Group:  As expected, really, really, Guo Ranruci, sure enough