Patanjali's yoga sutras

स्थिरसुखम् आसनम्
sthirasukham āsanam

sthira – steady
sukham – easy
āsanam—posture

The physical practice of yoga brings steadiness and ease.

Yoga isn’t always easy and you’re unlikely to feel very steady while trying to master a challenging pose, but the regular practice of yoga will, over time, create a lasting sense of steadiness and ease in your body.