I usually learn a lot from my mistakes and I might not be the brightest bulb on the tree but I've done well in life. You will too. Just don't ever volunteer! I learned that in Vietnam!
I'm definitely stupid, at times. One thing I've learned is that life tends to keep teaching us certain lessons over and over until we learn them. Since realizing this, I think I'm less stupid/stubborn/resistant to lessons. Or I try to be, at least.