Sthira-sukham-āsanam ( Patanjali's Yoga Sutras, chapter 2, sentence 46)

Meaning: Posture should be steady and comfortable

* 2 Essentials of postures: Yoga has been defined as the mastery of the thought patterns of mind field, so that Self-realization can be experienced. To be able to do the meditation practices that allow this, it is essential that the posture be steady and comfortable

* 2 Means of perfecting the meditation posture: prayatna-śaithilya-ananta-samāpatti-bhyām ( Patanjali's Yoga Sutras, chapter 2, sentence 47)

Meaning: Loosening of tension or effort to sit in the posture and allowing attention to merge with the infinite 

- Prayatna = tension or effort (related to trying to do the posture)

- Shaithilya = by relaxing, loosening, lessening, slackening

- Ananta = infinite, endlessness

- Samapattibhyam = by focusing attention on, by coalescence, coincidence, merging

SIT - STEADY - COMFORTABLE - FOCUS