Bhagavad Gita, Chapter 2, Verse 58

When, like the tortoise drawing in its limbs, he can fully withdraw the senses from their objects, his wisdom becomes steady.

Being able to pull your attention back in, on purpose, is its own kind of strength.

Indulging a craving doesn't quiet it, it usually feeds it. Real steadiness comes from being able to draw the senses inward at will, the way a tortoise pulls into its shell, rather than being pulled around by whatever's in front of it.