乘虛而入乘隙而入chéng xū ér rùenter through taking advantage of the unpreparedness; get a chance to step in; seize the opportunity to step in;take advantage of sb’s weakened position; break through at the weak point; hit when one’s opponent is off guard; exploit one’s opponent’s weakness
? 周人便趁著機會強大了起來，終竟～，把殷朝滅了。(郭沫若《屈原》 14)…this gave the Zhou people an opportunity tostreng then themselves until they were able to take the Shangs by surprise and conquer them. 乘虛而入chénɡ xū ér rù趁著某些薄弱的地方進攻。get a chance to step in, exploit one’s opponents weakness, break through at the weak point |