However beautifully we carry out an asana, however flexible our body may be, if we do not achieve the integration of body, breath and mind we can hardly claim that what we are doing is yoga. What is yoga after all? It is something that we experience inside, deep within our being. Yoga is not an external experience. In yoga we try in every action to be as attentive as possible to everything we do. Yoga is different from dance or theater. In yoga we are not creating something for others to look at. As we perform the various asanas we observe what we are doing and how we are doing it. We do it only for ourselves. We are both the observer and what is observed at the same time. If we do not pay attention to ourselves in our practice, then we cannot call it yoga.
T.K.V. Desikachar, The Heart of Yoga