1. I don't believe your "always."
2. Although your kids are no doubt very polite and nice, not all kids are like yours.
Never had it fail.
While true that it might have only been my kids and the way I raised them, I was raised the same way, in effect, and all my Dad had to do was say, "1,2........",. He never got to three.
Maybe it's genetic. ;^p
Some kids just don't listen.
Parenting IS important, no doubt, but there are always those families that have three kids, and two of them are exemplary students, well behaved, and one is a major jerk, screws off in school, and is the black sheep and he/she was raised by the same two parents as the other two kids.