I like trying to preserve my vassal noble houses , as well as my own dynasty. Once , when playing as Brittany , I had a House De Vitre. Through six generations the House De Vitre only once produced a son who lived to adulthood , and this was despite my giving four different members of that family four different counties. Trying to keep that family from going extinct was a real hassle.
--- But the plot thickens ; In ANOTHER game playing as Brittany I again wound up with the House De Vitre , same Coat of Arms too , and , AGAIN , the House De Vitre was notorious for turning out only females. In that game , too , in every generation I had to keep an eye on third daughters that I could marry off matrilleneally so the House wouldn't go extinct.
I know these are all strictly random dice roll types of things , never the less ........
In four different games I had to resort to adultery to save the House of El Cid because they were consistently infertile breeders.
In now five or six play throughs I have never failed to convert the first generation of children of the Merovingians to my culture . But , in five or six play throughs , it has never taken me less than five generations to convert the House of Welf to my culture.
* shrug *