Relaxation. Wei-wu-wei. Action by non-action, i.e. action by non-effort, which means no unnecessary effort, only using the minimum of effort required.

"A feather cannot be added; a fly cannot alight." A (physical) position is held so precisely , so delicately, that if a feather rests on the shoulders, the knee will need to bend because of the added weight. If a fly alights on the extended arm, the arm will drop.
The same principle applies to mental activity.