Honestly, I think this myth comes from our own insecurities. We hear a few positive things about what some other family is doing and we spin it into an image of:
A beautiful, meticulously-maintained home where the children cheerfully do what-they-ought 24/7 with never a whine or complaint (much less EVER hit or scream at the top-of-their-lungs). This family uses the perfect curriculum that is perfectly suited to all of their children and will ensure their children get accepted to the very best schools. Everyone always loves learning and feels like they get a lot accomplished each day and no one ever gets distracted from their lessons (or from over-seeing their children's lessons). Toddlers never bite their sisters while their mom is trying to read a story out loud. The kitchen is always clean and the table clear. As a matter of fact, clutter is completely non-existent. Bookshelves are perfectly organized and books are never left around for little ones or dogs to destroy. Books or car keys are never, ever misplaced, not even for a few moments, much less hours or days. Dinner is planned a week in advance and is always on the table when Daddy comes home and everyone is neat-as-a-pin for dinner. Dinner table conversation is always very lofty and is never interrupted by crying, whining, spilled milk or children falling out of their chairs. Crises or friends-in-need never jump in to take priority over planned lessons and a beautiful day never draws mom and children out-of-doors.
I've gone through my stages of insecurity and guilt (though I do certainly aim toward some of the above things). Now I'm quite comfortable saying: We are not that family and we don't want to be.