养痈成患

yǎngyōng-chénghuàn

(1) [a carbuncle neglected becomes the bane of your life-leaving evil unchecked spells ruin] 比喻姑息宽容坏人坏事, 结果受到祸害

真是养痈成患, 将来他的羽翼越多, 越难动手哩。 --清·李汝珍《镜花缘》

(2) 也说"养痈遗患"