It's a common subject of discussion between mothers how one's own children can be so vastly different from one another. I know why children who share the same gene pool, the same environment, and the same parentage turn out to be entirely different people -- it's nature's way of keeping their parents from getting becoming too self-satisfied with their own parenting skills.

You have your first child, you do things a certain way because you are convinced it's the best way, and things turn out pretty well. You begin to get a bit big-headed about it, thinking, "Behold! See what I and my superior parenting skills have wrought!" Then, inevitably, child #2 comes along and those unrivaled credentials do not produce anything close to the same results. Mother and Father are humbled, Child #1 continues to behave beautifully, as she would've naturally done even if she'd been raised by a pack of wolves, and Child #2 wreaks havoc and runs everyone ragged. It's the natural order of things.

Not that I know from experience, or anything.