śhrī bhagavān uvācha
prajahāti yadā kāmān sarvān pārtha mano-gatān
ātmany-evātmanā tuṣhṭaḥ sthita-prajñas tadochyate|| 55||

My Understanding : People with a steady intellect remain unaffected by external emotions. When they feel sadness, it doesn’t lead to excitement or excessive attachment to the sadness itself. You won’t see this outwardly because external fears typically cause sadness in others. However, when you do not hold opinions or attachments to particular things, there is no basis for sadness. As a result, you remain at peace and ultimately experience true happiness.