「乘虛而入」

(pos:語句)
<explanation>
yue:趁對方防範、準備不足嘅時候行動，令目標達成嘅機會提高
eng:to act when someone is unprepared; to break through at a weak point
<eg>
yue:賊人趁住户主返工，乘虛而入，偷走咗好多貴重物品。 (caak3 jan1 can3 zyu6 wu6 zyu2 faan1 gung1, sing4 heoi1 ji4 jap6, tau1 zau2 zo2 hou2 do1 gwai3 zung6 mat6 ban2.)
eng:Taking advantage of the owner being out for work, the thief broke into the empty house and stole many valuable items.