Parents are human beings. Humans make mistakes. This means that parents are not always right. Also, the fact that parents are older doesn't mean they are right. Adults tend to be more blinded by prejudice and other factors that a child is not usually affected by much. Finally, adults also have old beliefs and ideas that may be incorrect now and believe that they are right because they are addressing a child.
Now whether they are right most of the time or not is a different story, but, the fact is that parents can be just as stubborn as kids. When they think they are right, they really think that they are right. And so it boils down to this: the more knowledge we have access to, the more sure we are that we have knowledge that our don’t parents have, and the more we think it is our right to question our parents. So it gives the impression that extra knowledge can rival the experience of our parents.