I have friends who had a girl first (same age as my ds1), but very placid and easy-going; at first they were prepared to give me the parenting benefit of the doubt that maybe boys were different.
But then they have a boy (same age as my ds2), who is also malleable, compliant, and generally angelic at every turn.
They then become irritatingly smug parents, convinced that their children's good nature is entirely due to their wonderful parenting skills...
Then third child comes along ...
He is by no means a demon-child-from-hell ... he's just a normal, boisterous, at times hard-work pre-schooler.
But he hasn't half changed some of their smug attitudes