百不失一　

◎ 百不失一 bǎibùshīyī

(1) [cannot possibly go wrong;not a failure out of a hundred trials;never a failure in many trials] 一百次中也不会失误一次。形容极有把握,决不会出差错

从门应庭,听堂室之言,什而失九,如升堂窥室,百不失一。——汉· 王充《论衡》

(2) 又说“百无一失”