Excellent general advice.

Biden:

And by the way, I say to every young man looking to get married – marry into a family of five or more daughters. I did, my wife is the oldest of five sisters. You know why? One of them will always love you. Not the same one.

I don’t know about the specific rule, but the general principle is excellent advice and typically Catholic advice. Genes are assorted in one generation, but the same mix is likely to be available in a different generation. In a typical modern family your parents are your only resource. If you received genes that didn’t get expressed in your parents, you’ll be disliked and misunderstood by your parents. Their guidance, if they even care enough to provide it, will be wrong.

In a large extended family there’s a good chance that an aunt or grandfather will have the same personality, will understand you and give you appropriate guidance.

(And I’m speaking experientially of specific parents, a specific aunt and a specific grandfather.)