I think that ties in with issues of identity as well - that sometimes there are parts of us we want to hide, and then there's other times we say, "You know what? Nope. Done hiding that part."
And you're figuring out who you are, and you haven't yet become stagnant in your thinking. You haven't solidified. And one thing that I find is that a lot of grown-ups tend to look back on their high school or middle school years and say, "Oh, thank God all that's over."
If everyone started off the day singing, just think how happy they'd be.