True quiet means keeping still when the time has come to keep still and going forward when the time has come to go forward.  In this way rest and movement are in agreement with the demands of the time, and thus there is light in life.

Mountains standing close together: The image of KEEPING STILL, Thus the superior man Does not permit his thoughts To go beyond his situation.

The heart thinks constantly.  This cannot be changed, but the movements of the heart - that is, a man's thoughts - should restrict themselves to the immediate situation.  All thinking that goes beyond this only makes the heart sore. 

I Ching - Book of Changes