I wouldn't say it's impossible to understand. Imagine having a dog or other pet that you love ridiculously. Then one day the pet starts talking, reading, doing math homework instead of chewing your shoes as often.
I agree it's a hard comparison, but in my mind it's a difference of degree rather than class. Familial love is an awesome thing. It's lack in a person's life, when desired, can be heart breaking.
I wouldn't say it's impossible to understand. Imagine having a dog or other pet that you love ridiculously. Then one day the pet starts talking, reading, doing math homework instead of chewing your shoes as often.
It's a wild ride.