When the restlessness of the mind, intellect and self is stilled through the practice of Yoga, the yogi by the grace of the Spirit within himself finds fulfillment.
Sometimes our body is willing, but our mind is weak. Sometimes our mind is willing, but our body is weak. Do not be afraid. Strive to extend your capacity but do not be disappointed with yourself. What does not challenge us, cannot change us.
The battle of yoga is with the body and with the ego. You must conquer your ego, or small self, so that you can let your soul, your big Self, be victorious.