Upper trigram
☵
Water · Kan
Danger and depth.
FamilyMiddle son
ElementWater
Hexagram 3 of 64
☵☳ Difficulty at the Beginning
A hard start; growth held back by early chaos.
Lower trigram
☳
Thunder · Zhen
Arousal and shock.
FamilyEldest son
ElementWood
The image
Water above, Thunder below.
Water over Thunder: danger and depth meeting arousal and shock.
That combination is the whole meaning of hexagram 3. 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.