Is it forbidden for a layperson to contradict scholars? And why?

We Muslims are obligated to obey Allah and His Messenger. Part of obeying the Messenger is obeying the people of knowledge who are capable of deriving rulings from the texts of revelation, because they convey from Allah. Obedience to scholars is more obligatory than obedience to mothers and fathers, according to the text of the verse: "O you who have believed, obey Allah and obey the Messenger and those in authority among you." (Quran 4:59) "Those in authority" (Ulul-Amr) are the scholars, according to many Companions and Successors. Rulers are obeyed subordinately to the obedience of scholars. Thus, obedience is in what is good and what knowledge dictates. The common person must follow the scholar in matters of Sharia, based on the Prophet’s (peace be upon him) saying: "If I command you concerning something of your religion, then take it; and if I command you concerning something of my opinion, then I am but a human being."