千丈の堤も蟻の一穴より崩れる（せんじょうのつつみもありのいっけつよりくずれる）

Japanese vocabulary

Meaning: a small leak will sink a great ship

See it used in real works

• Example sentences from Japanese novels & web fiction (Massif)
• Hear “千丈の堤も蟻の一穴より崩れる” pronounced in real videos (YouGlish)