usually incompetence is the problem, not lack of intelligence

smart people make mistakes and misunderstand, 

dumb people make mistakes and misunderstand, 

incompetence is usually the problem 

intelligence is important for certain tasks: 

a person needs to be smart to do math, 

but there are lots of critical situations in life when math is not needed, 

but competence is needed 

usually incompetence is decreased by: 

learning by doing, 

training 

and education