Light entering into the earth means its brightness is extinguished; hence it is Darkening of the Light. The inner trigram is Li, and Li is the image of civilization and clarity; the outer trigram is Kun, and Kun is the image of yielding compliance.
As a person, one possesses the virtue of civilization within while able to maintain yielding compliance without. Anciently, King Wen was like this, hence it says "King Wen used this."
Facing the darkness of King Zhou was the time of Darkening of the Light; yet King Wen possessed civilized virtue within and served King Zhou with outer compliance, enduring great adversity without losing his inner luminous sagacity, which sufficed externally to keep calamity at bay.
This was the path King Wen practiced; hence it says "King Wen used this." In the time of Darkening of the Light, it is beneficial to abide in adversity without losing upright perseverance, which means being able to conceal and dim one's brightness.
If one does not obscure one's light, disaster will follow; if one does not hold fast to correctness, one ceases to be worthy and enlightened.
Jizi lived during the time of King Zhou, dwelling within the royal domain and in close proximity to the danger; hence it says "inner trouble."
Yet Jizi was able to conceal his brightness and maintain his upright resolve; this was the path Jizi practiced, hence it says "Jizi used this."