Upper trigram
☶
Mountain · Gen
Stillness and limit.
FamilyYoungest son
ElementEarth
Hexagram 41 of 64
☶☱ Decrease
Giving something up for a larger gain.
Lower trigram
☱
Lake · Dui
Joy and openness.
FamilyYoungest daughter
ElementMetal
The image
Mountain above, Lake below.
Mountain over Lake: stillness and limit meeting joy and openness.
That combination is the whole meaning of hexagram 41. 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.