Why do teenagers think they're mature when they're actually not?

[Michelle]

For instance, I was friends with a 14-year-old girl on Facebook. I had been sharing a lot of stuff with her on her profile (mainly videos) and trying to help her with articles she's been writing for some website (it's more than likely a spam website). Apparently she was annoyed by sharing so many things with her (I was only doing it to be nice) and thought I was criticizing her work. Anyway, yesterday I found her Twitter page and she said really mean things about me behind my back. I sent her a message on Facebook calling her on everything she said asking her why she said these things when I never did anything bad to her. She responded by blocking me. What I don't get about this whole thing is why she's claimed she's as mature as an adult (she said this in one of her notes on facebook). If she were actually mature, then she should have sent me a message asking me to stop posting things on her wall instead of saying stupid things about me behind my back.