用冷水泡的柠檬不会酸
[yòng lĕng shuĭ pào de níng méng bù huì suān]
Translating literally it means 'A lemon soaked in cold water isn't sour.' This is a metaphor that can have various interpretations, but generally suggests maintaining composure or not showing weakness in challenging situations. In another context, it could mean desensitization or growing accustomed to harsh realities, hence no longer feeling 'sour'.