Bhagavad Gita 2.56
दुःखेष्वनुद्विग्नमनाः सुखेषु विगतस्पृहः। वीतरागभयक्रोधः स्थितधीर्मुनिरुच्यते॥
Easy meaning
A steady mind does not panic in pain, or cling wildly in pleasure. When craving, fear, and anger loosen, calm becomes possible.
When to use
When worry spirals and you need one clear breath.