I. Q. deficiency. There are some people who are an order of fries short of a Happy Meal, and what is often a characteristic about every one of these people is that they don't know it. They have no idea how incompetent or stupid they are. It's the exact opposite. They have the loftiest, highest self-image.
Parents find many different ways to work their way through the assertiveness of their two-year-olds, but seeing that assertiveness as positive energy being directed toward growth as a competent individual may open up some new possibilities.