one careless match can start a forest fire
Definition:  circumstances in which a small action or change that does not seem important but has a very large effect
Usage:  Donald thought he was just innocently making fun of bill, not knowing that bill is battling with chronic depression; later than day bill committed suicide; when they heard this, they realised that one careless match can start a forest fire

SEPEDI
Translation:  lehlokwana le tee la go se hlokomelwe la mankhwari le ka thoma mollo wa sethokgwa
Proverb: pšhišamadiba e pšhiša a magolo

XITSONGA
Translation:  ritlhongo rin’we leri nga languteriwangiki ri nga sungula ndzilo wa nhova
Proverb: n'wana wo pfumala nawu i khombo etikweni

TSHIVENḒA
Translation:  ṱhogwa ḽithihi ḽi si na vhulondo ḽi nga thoma mulilo u fhisaho ḓaka
Proverb: mulomo ndi muloi