Why do they grow up and show us ourselves?

We've all heard every parent lament about how we so wish our kids would grow up (some days), and lo and behold they do. Then we are sad that they've grown and want them to be little again, right? Some days, we wish they could act more maturely, think more maturely, and understand things in a more mature way. So I give a resounding yes to all of this, but tonight I saw another aspect in my child that made me think of another reason we kind of resent this growing up thing our kids do. It goes beyond the "Awwww, remember when you were little and......" moments. As they do grow, they have more sophisticated ways about them, and that includes how they get angry. There was a minor dispute tonight between Dad and child. Child then becomes enraged, I mean like name calling her dad and wishing she could toss something at him kind of enraged over a really teeny tiny thing that he had done in jest. She then goes into a 20 or more minute pout, an angry pout. So then I, super mom, decide to let her cool down. All the while I am boiling and frustrated at her. So I go upstairs, chew her a new rear end, come downstairs and have an epiphany. I told her she needed to grow up, but lo and behold, she already has. She is having a big girl tantrum, very similar to the ones that ....ummmm.....I have. I saw myself in her. Long and short of it, child was frustrated throughout the day because she is on a semi-grounding which is rather undefined. So with the various requests that came from her lips today, we considered and then gave them all a "No." Amazingly, she seemed to roll with it pretty good, but what I think happened tonight is a girl who really was mad at mom and dad all day, but never really put her finger on it. And in the end, it came out backwards, and those that she loves end up being hurt. I do this all of the time, and I soooo saw myself in my young lady tonight. WOW, they do grow up and become just like us....even in the icky ways :( Note to self: deal with the frustration at the start, and then the ones I love don't have to suffer later!