You look back on the stupid shit you used to do and then you look at yourself now and you're like "Wow! I really have come a long way, baby!"
And you compare your reactions then with your reactions now and you're so proud of yourself and you run around yelling about it because you want the whole world to know how much you've grown up.
But then you turn around and do something stupid and suddenly you're questioning whether you've actually learned anything at all.
(And when I say "you," I mean me. As if you had any doubt.)