if he has considered a question and come to a conclusion, finding that others, even others whom he respected, disagree with it, this does not modify his opinion regarding the question, as Robin said, but his opinion of the other person

When there is a disagreement between your opinion and that of another person, we need to carefully seek out evidence to tip the balance.

Problems arise when we start treating the fact that we hold opinions as evidence in favor of those opinions. It is extremely important to maintain the correct hierarchy of reason: no conclusion reached by an argument that takes certain premises for granted can be used in an argument in which those premises are the conclusion.

If you always presume that your every whimsy is correct, people will become tired of arguing with you, and your errors will never be rectified.