one’s plan is foolproof;a completely safe (/a surefire) plan ❍ 自古道： “欲令智昏”。贾琏只顾贪图二姐美色，听了贾蓉一篇话，遂为～，……(《红楼梦》837)As the old proverb says，“Lust befuddles the mind.”Jia Lian was so infatuated by Second Sister’s beauty that he felt Jia Rong’s plan was foolproof.
计出万全ji chu wan quan
foolproof plan
计出万全jì chū wàn quán
计：计策；万全：稳妥、周密，万无一失。比喻计策稳妥、周密，不会出现意外情况。one’s plan is full-proof, a complete safe plan