Can we achieve the perfect asana, or yoga pose? What is the perfect yoga pose? Is it important to work toward the perfect pose?
The "ideal" classical form of any pose, as shown by high level yoga practitioners, won't be accessible in that same form by most people, especially those who are older and stiffer, or who have various health and mobility issues. They'd injure themselves if they forced their bodies to conform to what we might consider "the perfect pose"! But that doesn't mean they should stop working toward the ideal pose for their own body, even though the shape or emphasis of that ideal pose will change over time.
That makes sense, of course. Consider the poses you see on the cover of Yoga Journal, or in the YJ calendar. These are beautiful poses done by young, fit people. But as we age, our body obviously changes, and our strength and flexibility will diminish. But our awareness of our bodies grows as we continue our practice, and we can work more intelligently in the poses even though we might not be as strong or flexible as we once were.
In the Yoga Sutras of Patanjali, two sutras especially speak to this:
II: 46 Sthira sukham asanam
Or as translated by B.K.S. Iyengar in Light on the Yoga Sutras of Patanjali, "Asana is perfect firmness of body, steadiness of intelligence, and benevolence of spirit." He comments that, "whatever asana is performed, it should be done with a feeling of firmness, steadiness and endurance in the body, goodwill in the intelligence of the head, and awareness and delight in the intelligence of the heart." and "in any asana, the body has to be toned and the mind tuned so that one can stay longer with a firm body and a serene mind."
II:47 Prayatna saithilya ananta samapattibhyam
or "Perfection in an asana is achieved when the effort to perform it becomes effortless and the infinite being within is reached." He goes on to say, "perfection must be attained through perseverance, alertness and insight. Without these we remain dull and make no progress." But the struggle to perform the asana is gone, while we maintain our firmness of body, intelligence of mind and benevolence of spirit. There's a balance between effort and relaxation (such that it is) in the pose.