Okay well here's a crude example
Introverted "bookish" academic type parents have one introvert child and one extrovert child.
Now I know many lovely wonderful introverts (who are totaly worth the LOOOONG amount of time it takes to gain their friendship) who absolutely HATE going to playgroups or playdates or anything to do with school gates etc, but do it for the sake of their children if that's what the child wants/needs.
But for the sake of this example, these particular parents don't do any of the above, and continue to like to close the door to the world and have a quiet life and don't make any concessions for their extravert child. Not all parents treat all their children well.
Now the children grow up, and as you do, when they meet their future partners, they tell them about their lives/upbringing:
Introvert adult child: My parents are lovely people, home was my refuge from the world, they never forced me to be outgoing and always took an interest in my reading and my projects, they'ld sit for hours reading with me or doing my puzzles/models, you'll like them, they're really calm and lovely. My brother was always a bit of an attention seeker though he was always damaging my stuff we weren't really close growing up, he always seemed to throw a spanner in things and was always breaking my models. He was always trying to make everything about him and acted out
Extravert adult child: I never really "fit" and my parents never really accepted me for who I am, everything was geared up around their interests and my brothers interest, there were lots of books and model building but I was never taken to football practice or anything sporty or social, I was really lonely at home, my parents didn't like the noise and mess of playdates so I wasn't really able to have friends over. I was really bored and lonely but always got told off if I tried to play with my brother because his reading/model building, he was their favourite and my interests didn't really get a look in. I was always negatively compaired to him. I really missed having people and activity about so when I was a teenager I went after that in all the wrong places. My parents were never interested in getting to know my friends parents so they never really knew what was going on in my life and I ended up getting into a lot of trouble.
Which is why this idea that "oh I have a "nice" adult child/SIL/DIL so it can't be my fault and must be because of DIL etc" is not something I buy, personally.