When our kids are little, it's so easy to joke about how are kids will be as teenagers. I think most of us are guilty of saying things like "until they're a teenager and don't listen to me at all". The brutal truth is; those teenage years do come. All of the little things we previously joked about are suddenly coming true, and more, for most of us. However, it's not funny. It's so easy to get hurt by your teenager. It's all to easy to cry at the actions of your teenager; your once sweet baby that you swore was destined for greatness.
To hear moms of young children complain about not sleeping because of a baby or terrible twos becomes the new joke to the parents of teenagers except down deep we're actually envious of the lost, simple, years we didn't enjoy enough. We wonder if we're simply repeating that mistake with our big kids (young adults). The problem with teenagers is the worries are so much bigger. The mistakes they make are consequential to the rest of their lives unlike toddler grievances. Little kids can make you feel bad, but no one can make you feel like a more of a failure of a parent than your young, very independent, adult.
Our jobs now, and its a tough one, is to try really hard not to let it get to you. That's my biggest failure or weakness. Your call.