To be dumb is to be wrong about most things you should know by your age! It's not when you're wrong about one or two things! For example, if a 30 year old didn't know any math at all, then their considered dumb, or stupid! Not like if a 1st grader doesn't know the answer to 1+1! Then it's considered that the child needs to learn more math! So if you don't know one or two things you should or shouldn't know by your age, then you're definitely NOT stupid, or dumb!