Upper trigram
☱
Lake · Dui
Joy and openness.
FamilyYoungest daughter
ElementMetal
Hexagram 31 of 64
Mutual attraction, courtship.
Upper trigram
Joy and openness.
Lower trigram
Stillness and limit.
Lake above, Mountain below.
Lake over Mountain: joy and openness meeting stillness and limit.
That combination is the whole meaning of hexagram 31. 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.