出其不备

Explanation: Refers to actions contrary to people's expectations 　　Usage: Verb-object type; for the predicate; with compliment 　　Source: Qing Cao Xueqin's "Dream of Red Mansions" 73 back: "This is not Taoist magic, it touches on the most intensive use of troops in the so-called 'defensive such as Virgin, out of such as rabbits', 'out of it is not prepared' the medication." Thesaurus:  Happen unexpectedly, By chance Ing, upset, unexpectedly, against expectation, s unpreparedness, The enemy accident