小洞不堵，大洞難補 [－－－－－－－难补]

Jyutping siu2 dung6 bat1 dou2 , daai6 dung6 naan4 bou2
Pinyin xiǎo dòng bù dǔ , dà dòng nán bǔ

Definitions (CC-CEDICT)
  1. If you don't plug the small hole, the big hole will be hard to repair (idiom); A stitch in time saves nine.