Why do I hold my convention at the moment of the Summer Solstice? Because it is a change in pattern that is observable. Observation directly linked to survival. Think of the Incas in Machu Picchu, their observation of the Solstice was the basis for timing the planting of the crops.
In my style of Pilates, the "spirit" in Joe's definition of Contrology as "Complete coordination of body, mind and spirit" is the observer/listener. The observer/listener is not the thinker. So, to get the complete coordination of body, mind and spirit, spirit has to be present and completely coordinated with body and mind.
You have to listen; you just can't go from mind to muscle. (well, you can, and many do, but if you do it's not my style)
You have to listen to what you sense and make change based upon what you observe. You have to own your effort to control your movement. And that takes engagement of the observer/listener. Spirit. Observation. Control. Survival.