Bhagavad Gita, Chapter 6, Verse 7

To the self-controlled and serene, the Supreme Self is the object of constant realisation, in cold and heat, pleasure and pain, as well as in honour and dishonour.

Real mastery here doesn't mean nothing ever happens to someone, it means those swings stop controlling them.

Heat and cold, praise and blame, these things still happen to a mastered mind, they just stop dictating its state. That steadiness through genuinely different conditions is what real conquest of the mind actually looks like.