Upper trigram
☰
Heaven · Qian
Creative force.
FamilyFather
ElementMetal
Hexagram 33 of 64
☰☶ Retreat
Withdrawing in good order before it is forced.
Lower trigram
☶
Mountain · Gen
Stillness and limit.
FamilyYoungest son
ElementEarth
The image
Heaven above, Mountain below.
Heaven over Mountain: creative force meeting stillness and limit.
That combination is the whole meaning of hexagram 33. Nothing about it is arbitrary — change either trigram and you get a different hexagram with a different reading, which is why the 64 form a system rather than a list.