Kids always think they "know it all"......unfortunately the things they "know" all comes from idiotic TV shows like Teen Mom and Jersey Shore........even if they say they know, MAKE SURE you still try to get the point across that you were trying to make, that way you know you tried so that when they still go out and mess up, you can say "I told you so" 8)
Since I'm a kid, I'll answer. Sometimes it's what Tony said. I don't want to admit that I didn't know that, so instead I try to almost reassure her that I know what I'm doing and don't need my hand held. Other times it seems like she repeats herself ALL THE TIME!!!
I think its a combination of all of these answers, how ever i would like to add, some times its a defensive answer, a few parents can with out realizing it state things in an abrasive way to kids, and some times we make them feel stupid with out meaning to. Im not saying coddle the children but we can step back and take a breath before we snap our answers out.