Ignoring this fact gets people into trouble in all walks of life from couch potatoes to elite athletes. Relative stiffness and flexibility are especially important in yoga where we are looking for a balance between the two. This concept was very simply and effectively explained to me by Shirley Sahrmann, one of the greats in the world of Physical Therapy. She took two metal springs. One was less stiff (a smaller spring to make it obvious) and the other was more stiff (a larger spring). She linked the 2 springs together in series (end to end) and pulls on both ends. Which spring deformed a greater distance? Well it was the less stiff spring, of course! Because it took less force to deform or stretch the less stiff spring, that is the one that moved first and most.