Not very smart

Have you ever done something like, say, hit your thumb with a hammer? Sure you have. Ever have someone then make the comment "Gee, I'll bet that smarted!"? I'm betting you have. If you're like me (God help you) you must have wondered how in the world that saying came into being. I mean, whatever you did that resulted in pain obviously wasn't smart, right? So why is it that when you do something like hit your thumb with a hammer, or try to pick up a hot muffler with your bare hands, or check a knife's sharpness by running your thumb over it, we use an expression with the word "smart" in it?