“When the energy is strong, one can go to the sea; when the energy is weak, one must go to the mountains.” This reflects the ancient understanding of the rise and fall of “energy.”
“Energy” can be understood as life force or the state of fortune.
Why go to the mountains when energy is low?
The mountain represents yang, strength, and stillness. The mountain's towering and steady presence allows energy to rise and disperse outward.
When a person is low in energy and depressed (weak energy), what is needed is uplift and support. Climbing high to see far and absorbing the strong energy of the mountains helps stabilize the mind and regain upward strength.
If one were to go to the sea at this time, the sea represents yin, softness, and entrapment. The vastness and depth of the sea might amplify feelings of powerlessness and confusion within, hence the metaphor “it is easy to fall into the water when observing the sea with weak energy.”
Why go to the sea when energy is strong? When a person is full of energy and feels accomplished (strong energy), what is needed is restraint and settling. Facing the vastness of the sea instills a sense of awe, teaching one to be tolerant and humble, redirecting and collecting the overly extroverted “strong energy.” At this time, if one were to climb the mountains, it becomes easier to foster pride and impulsiveness at a high place; the saying goes, “the heights are hard to bear,” and one might carelessly “fall off the cliff” due to excessive confidence.