The winter solstice has always been celebrated in China as the resting time of the year… In winter the life energy, symbolized by thunder, the Arousing, is still underground. Movement is just at its beginning; therefore it must be strengthened by rest
Wilhelm’s commentary presents the Winter Solstice as the archetypal moment when nascent life-energy must be guarded from premature dissipation through deliberate stillness and rest.
, The I Ching or Book of Changes, 1950thesis