Yichuan YizhuanLine statement
The fourth line is the master of establishing trust. Occupying a position close to the ruler, dwelling in correctness, and enjoying the utmost trust of the superior, it shoulders the responsibility of sincere trust.
It is like the moon approaching the full: the zenith of fullness. Once completely full, it rivals the sun; when a minister rivals the sovereign, disaster and ruin inevitably follow, which is why 'nearly full' is taken as the supreme state.
'The horse's mate is lost': the fourth and the first are in proper correspondence, being mates.
In ancient times, four horses drew a chariot; if a single pure color could not be obtained, the two inner horses shared one color and the two outer horses another, and their sizes had to match. Thus two horses formed a pair (pi), meaning counterparts.
Horses are creatures of motion; the first line responds upward to the fourth, and the fourth also advances to follow the fifth, both moving upward—hence the horse is taken as an image.
The way of trust requires singleness: once the fourth follows the fifth, if it still looked down and attached itself to the first, its loyalty would not be single, harming sincere trust and bringing blame. Therefore, when the horse's mate is lost, there is no blame.
Ascending to follow the fifth without being bound to the first is losing its mate; being tied to the first, it could not advance and could not achieve the work of trust. The Image says: 'A team of horses lost: it severs ties with its kind to ascend.'
It severs ties with its fellow kind to ascend and follow the fifth. 'Kind' refers to its correspondent.