one’s plan is foolproof;a completely safe (/a surefire) plan ? 自古道： “欲令智昏”。賈璉只顧貪圖二姐美色，聽了賈蓉一篇話，遂為～，……(《紅樓夢》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.
計出萬全ji chu wan quan
foolproof plan
計出萬全jì chū wàn quán
計：計策；萬全：穩(wěn)妥、周密，萬無一失。比喻計策穩(wěn)妥、周密，不會出現(xiàn)意外情況。one’s plan is full-proof, a complete safe plan