It also has to do with the evaluation of the motivations that guide action. Wisdom is partially spawned by notion of Right Action in the Eight-fold path. The important thing is that the back should be straight and unsupported, and lightly balanced on the pelvis. The head should be squarely balanced on an upright neck. The eyelids are lowered, and the mouth is lightly closed.
Reality is but a illusion created by our unenlightened minds.
It is also a part of this reality that all is in flux, rocks become sand, people become dust. All is impermanent, even the Dharma itself. But finally is the reality that we, as individuals do not exist outside of the life energy that creates us all. There is no Buddhist notion of an individuated soul, or some entity distinct from any other living thing. We are all part of the energy, not distinct pieces.