You will often hear the term mind-body in reference to yoga. This mindset is spiritual, almost mysterious in itself. From my experience this is an awareness of yourself so much that you find yourself able to achieve great strides in your postures. It is finding the mental connection to the pose; maybe it is confidence in yourself. I do not know but when it happens to you, it is mysterious.
Yoga speaks a lot about listening to yourself, listening to your body. Not pushing it when it feels pain but also, gently relaxing into poses. For those who do the same posture time and time again, and cannot move further, the key is sometimes relaxation. You allow the exhalation or relaxation that comes with your exhalation to lead you further into your each pose.
It always amazes me how they taught us to adjust people in postures. It only takes a light touch on someone to guide them where they already know to go in their postures. Yet you find yourself bending in ways you did not know were possible.
It is like they have some sort of invisible string attached to you and the lightest touch gives you the courage to try things you would not have tried before. And yet it was inside us all along.