It might be part on watching the mom's reactions. Seems that females tend to imitate their mothers/grandmothers more. With our barn cats, most of the females were shyer or less tolerate of new cats compared to the males.
My female rexes (I had 2 breeding) - one was pretty tolerant in shows and most of her kittens (males especially) were easy going. Spooky's sister hated shows and I showed a few of her daughters - they didn't like them either....yet the males were fine.
I don't think about it too much - too hard to figure out