Nothing can be cuter than two or three year olds absolutely insisting they know something is right when they have it entirely confused. It doesn’t matter how much evidence you provide that they are wrong, this child (not yours or mine of course) will stubbornly stick to the original statement. Most parents eventually shrug it off and figure over time the child will learn he is incorrect and will change his mind.
Unfortunately, many children never outgrow this habit. They read something somewhere or hear it from someone they admire or sometimes just figure something out independently. No matter what evidence you provide to the contrary, they will not even consider another viewpoint. Throw in a bit of adolescent indestructibility with a dash of “old people are stupid” and you have a recipe for arrogance and pride.