小洞不堵，大洞难补

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

small / tiny / few / young

cave / hole / zero (unambiguous spoken form when spelling out numbers) / CL:個|个[ge4]

no; not so / (bound form) not; un-

to block up (a road, pipe etc) / to stop up (a hole) / (fig.) (of a person) choked up with anxiety or stress / wall (literary) / (classifier for walls)

see 大夫[dai4 fu5]

big; large; great / older (than another person) / eldest (as in 大姐[da4 jie3]) / greatly; freely; fully / (dialect) father / (dialect) uncle (father's brother)

difficult (to...) / problem / difficulty / difficult / not good

disaster / distress / to scold

to repair / to patch / to mend / to make up for / to fill (a vacancy) / to supplement