“The study of asana is not about mastering posture.  It’s about using posture to understand and transform yourself.”
B.K.S Iyengar

Although yoga comprehends so much more then just asanas, this is the aspect we mostly focus on in the West. I think this quote from B.K.S. Iyengar covers a very important principle of the yoga practice: it is not about the end position, but about the journey towards it.