Definition of HIERARCHY:
any system of persons or things ranked one above another.
The first born and eldest son takes priority, then his offspring, their offspring etc etc.
Second in line is also a son, but he doesn’t hold the same importance, as there’s already one of those.
Comes the first daughter. Important in her role for her sex, immediate potential for grandchildren.
Finally another daughter, quiet, always in the shadows of everyone else, but caring, loving, and considerate of others.
Move on fifty years.
The first born has offspring, each having their own families. The family name is secure.
Second son also has a family, and there is another generation there too, but little is said.
First daughter has 2 daughters, the eldest also has 2 daughters, the eldest of which has a son. Another family name will continue.
Second daughter has no children, but continues to care, love and consider all family members. Sadly all family members bar one have no interest.
Like the Royal Family, as more children are born into other lineages, the fourth child is pushed further and further down the line of thought and succession until they disappear from it altogether.
On their tombstone will read:
Here lies the fourth child.
No more hurt to endure.
No generations to follow,
No hierarchy to obey.
pensitivity101 
That’s a sad tale.