Upper trigram
☵
Water · Kan
Danger and depth.
FamilyMiddle son
ElementWater
Hexagram 8 of 64
☵☷ Holding Together
Union around a shared centre.
Lower trigram
☷
Earth · Kun
Receptive yielding.
FamilyMother
ElementEarth
The image
Water above, Earth below.
Water over Earth: danger and depth meeting receptive yielding.
That combination is the whole meaning of hexagram 8. 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.