Perfection in asana is achieved when the effort to perform it becomes effortless and the infinite being within is reached.
It took me many years to realize my own translation of the translation of the Yoga Sutra 2.9 above. You don't have to master the pose you see on someone else's body to experience effortlessness in your own posture. I used to believe that effortless state could be reached when I could master a posture someone ancient or otherwise had come up with. It was outside of my perception that effortlessness is relaxation. In fact, it took me years to learn how to relax. I couldn't stomach or had a stamina for long term projects, works, and relationships. Once I settled into the yin and restorative practices miraculously overtime everything fell into place and I began to experience effortlessness in all areas of my life. If you are busy making your body fit a pose (or a certain image) you cannot allow the pose (or your current life condition) to fit your body. Without the unity between your body and the pose you cannot reach effortlessness.
The body is self-possessed and self-mastery. It has the ability to do exactly the amount needed to be done for itself. The problem is the mind projects otherwise and the subconscious enslaves the body to do what it craves. The cravings feed the stress-response which feeds the habits that make up the habitually divided--struggling and wounded self. The Buddha put the habits of disconnect under the Five Hindrances--desire or greed, aversion or ill will, sloth & torpor, restlessness & anxiety, and doubt or lack of faith. They arise when an effort is directed unskillfully. Experiencing the Five hindrances chronically leads to a constant interference in your homeostasis. Instead of building you up the effort is tearing you down. Once you establish yourself deep in the hind zone it hinders you no matter what condition you find yourself in. You are swept in what the Buddha called the Eight Worldly Winds or vicissitudes.
Being a victim of gain & loss, praise & blame, fame & disrepute, and pleasure & sorrow simply means you aren't their beneficiary. Why not? Everybody experiences the vicissitudes. Only those who know how to use their effort wisely benefit from the constant unfolding of the dual reality. Duality is the movement of balance from effort to effortlessness. Yogic awareness or mindfulness transforms the subconscious reinforcement of hindering into surrendering into freedom of movement that is wise effort. It takes a lot of struggle to not be your effortless self. Let your wearied self be held through mindful relaxation. Here are how your effort can lead to effortlessness that leads to sustainable effort or stamina:
1. Relax the senses inside the mind: tune the senses to the inside of the skull; allow the eyeballs to release into the back of the sockets; soften the forehead and temple so the eyeballs and eyelids can sink into the forebrain; relax the gaze with the eyelids 3/4 way down or closed; soften the tongue and release its base down; relax around the teeth; feel the wind of breath inside the nostrils; soften the cheeks and jaw; feel the vibration of sounds inside the skull; allow each breath to rest your senses deeper inside the spaciousness of the wakeful mind
2. Relax the mind inside the heart: tune the mind to the chest cavity; soften the content inside the chest; allow the shoulder blades to drop away from the ears without collapsing the chest or spine; feel the motion of the breath at the upper back, shoulders and chest; let them rise and fall freely; connect to the flow inside the spacious heart
3. Rest the heart inside the gut: tune the breath along the spine; when the body is relax allow the inhalation to lift the heart organ up and the exhalation to release the heart organ toward the soft belly; when the body is muscularly active keep the belly tight but the chest soft -- inhale into the back, side, and top of the lungs, exhale by pushing the navel in to expel the air out but keep the chest soft and release the heart toward the belly; allow the mind to rest inside the heart; allow the sense organs to rest inside the mind
4. Relax the gut inside the gravity: tune the breath along the spine; when the body is relax feel the belly, pelvic floor, legs and feet release toward or against the solid ground -- let the bones and the belly soaked in the gravity; when the body is muscularly active keep the belly tight by pulling the gut content, the tailbone and heel bones downward through pressing the sit bones and the adductor muscles into each other -- allow the pressure to root the feet, legs, and abdomen down toward the earth; allow the heart to rest inside the gut; allow the mind to rest inside the heart; allow the sense organs to rest inside the skull
May your effort to unite within leads you to effortlessly unite with all that exists in your unfolding experience.