The answer is the great fear they have that they are not smart enough to succeed. The solution is to keep trying, regardless of fear and even failure.
Never give up! Giving up because you fear failure or are already convinced you will fail does only one thing – it guarantees failure. Almost every successful person built their success upon a mountain of failure, but no one else ever sees that; all we see is a successful person on top of the world.
Never give up! A failure is a learning opportunity. Keep trying and fail again a new way. Each time you fail, your brain is learning. Remember how you learned to ride a bicycle as a child. You fell! (Failed!) You got back on and fell again! (Failed!) You continued to fall (Failed!) (Failed!) (Failed!) (Failed!) (Failed!) (Failed!) (Failed!) But suddenly you were on the bicycle and wobbling but not falling! (Success!) From that point on you rode with confidence and fell only if an unforeseen occurrence happened, such as loose rocks on the road.
As a child you trusted your brain. You had no doubt that if you kept at it, you would learn to ride. Apply the same lesson to everything you need to do and to learn. Never quit, never give up, and you WILL SUCCEED!!!