The older I get, the dumber I'm becoming.
When I was a teenager, I knew practically EVERYTHING!
When I was a kid, older and taller people were constantly telling me how smart I was. (I wasn't, by the way. I just knew how to listen and pay attention. And I knew how to use big words like “arachnid” and “anarchy” from reading so much. What a nerd!)
In a post-school world, I've found that people actually do not usually care how smart you are. They care about how you treat them, how much you listen versus speak when they want to tell you something, how confident you are, and, to some degree, how much experience you have.
As I focus more on these things, I find that I no longer care, either, how “smart” I am.