张而不弛,文武弗能也;弛而不张,文武弗为也。一张一弛,文武之道也。· Even the Kings Wen and Wu could not remain tense without any relaxation. Neither would they allow themselves relaxation without tension. To be alternately strung and unstrung was the course they followed.
· Tension without relaxation is unbearable even for Kings Wen and Wu. Relaxation without tension is not what the kings have preferred. Their principle is to alternate tension with relaxation.
(The Book of Rites [of the Warring States Period])