Movement and Entropy

At the beginning of a meditation session, I adopt a good posture with my spine erect. Then after a few minutes I find I lost it and need to straighten up again. Why is that happening?

I think the breath acts likes waves on rocks, eroding the tight structures and bringing them to the point of least resistance.

Three things from this:

One, nothing is static in this universe, everything is in constant movement.

Two, that movement carries within the power to dissolve.

Three, keeping form, keeping geometry, becomes a daily effort, a constant struggle, an endless exercise of will and presence.