The gunatita treats happiness and sorrow with the same even gaze. A lump of earth, a stone, and a bar of gold hold the same value in their eyes. Praise does not inflate them. Blame does not deflate them. They are dhira — firm and stable in understanding.
This does not mean they are emotionless or detached from the world. The key word is "svastha" — situated in the Self. Their centre of gravity is within. When your sense of who you are rests on something eternal and unchanging, the ups and downs of external life lose their power to destabilize you.
"Svastha" is a remarkable word. It literally means "situated in one's own Self" — sva (self) + stha (established). In everyday Hindi, svastha means healthy. The Gita is suggesting that true health is self-abidance. When a person is anchored within, they are naturally steady, naturally well.