面具下掩饰的悲伤
[miàn jù xià yăn shì de bēi shāng]
The phrase means “Concealed sorrow beneath the mask,” reflecting one's inner feelings covered by a superficial demeanor. It shows the contrast between what others may see – happiness or indifference - versus the person's actual sadness hidden within, suggesting they are pretending for appearances sake while carrying internal distress or grief.