xì​dà​qiáng​huài

small problems lead to big disasters

隙大墙坏 隙大牆壞 xì​dà​qiáng​huài
small problems lead to big disasters
Literally means that when cracks in a wall become too large, the wall will collapse. It is a metaphor for how neglecting small faults or errors will eventually result in a major catastrophe. It is often cited from the book 商君书 shāng​jūn​shū.