Bhagavad Gita 2.56

The one whose mind is not overthrown in sorrow, who does not run after pleasure, who is free from grasping, fear and anger — that one is called a person of steady wisdom.

दुःखेष्वनुद्विग्नमनाः सुखेषु विगतस्पृहः ।
वीतरागभयक्रोधः स्थितधीर्मुनिरुच्यते ॥

duhkhesv anudvigna-manah sukhesu vigata-sprhah |
vita-raga-bhaya-krodhah sthita-dhir munir ucyate ||

The one whose mind is not overthrown in sorrow, who does not run after pleasure, who is free from grasping, fear and anger — that one is called a person of steady wisdom.

This verse gives us a lifelong goal to work toward, not a test you have to pass perfectly today. Being mentally healthy does not mean you never feel sad, angry, or afraid. Sorrow and pain are normal parts of life. True mental health is simply about feeling those difficult emotions without letting them permanently break or control you.