The distribution of Wist aptitude.

Rita and Jhames were the top in their field. They fell in love with each other, each captivated by the other's skill and talent for magic. They had seven children over their life, and only a single one had even a wink of talent like their parents.
This is because of the fundamental cycle and paths Wist takes before it connects with someone's soul. Wist is not created when the child is born, but their potential slips into them through the mother's womb and builds until the baby begins to think, and identify the world.
The connection's one can have to wist come in three main varieties.
The first is a stubborn and weak connection, found in children of great and incapable mages alike. We shall mark it as 1.
2's come next, and have a more focused and capable ability, though they do not number as greatly as the 1's.
3's are the most powerful of this trio, and born in only specific circumstance.
Behold the pattern
1 + 1 = 2
1 + 2 = 1
1 + 3 = 1
2 + 2 = 3
2 + 3 = 2
3 + 3 = 1
Three ways to make 1, two to make 2, and only one way for a 3 to be born; a child of two 2's.
In shorthand
If they match, go to the next rank, if not, the child takes the lesser rank.
1's are unlucky, they find life sapping away before 60.
2's are natural, they die out just before 90.
3's are truly great, they live to 120 years.