Have you ever thought you are dumb because someone else can do something you can't do ?
I felt that way once! You see, I play soccer and I'm not good at running. But there's a girl on my soccer team and she's great at running! But there are things I am great at doing, like defense!
See God did not make everyone the same. People are different in many different way's! Don't compare yourself to other people because God made you in your own special way.
So if you think your really bad at something just practice at it and sooner or later you will do it!