千里之堤，溃于蚁穴

qiān lǐ zhī dī , kuì yú yǐ xué

lit. an ant hole may cause the collapse of a great dike (idiom)

fig. huge damage may result from a moment's negligence

千

qiān

used in 鞦韆|秋千[qiu1 qian1]

里

lǐ

li, ancient measure of length, approx. 500 m

之

zhī

(possessive particle, literary equivalent of 的[de5])

堤

dī

variant of 堤[di1]

，

,

溃

kuì

(bound form) (of floodwaters) to break through a dam or dike

于

yú

(of time or place) in; at; on

蚁

yǐ

ant

穴

xué

cave