Here's an interesting article by John Tierney of the New York Times on how Facts are No Match for Gossip. Some interesting experiments and studies have been conducted to document this and Tierney references them in the article.
I'm no scientist so I can't speak with the authority Tierney and those he cites, do. But I wouldn't be surprised if I am not the only one who has experienced the triumph of gossip over facts/truth, in practice.
It seems that no matter how well-reasoned or documented an argument may be, gossip, if available will be more persuasive. I have seen this in many situations. It usually goes like this - you present your case but the other remembers hearing someone who said thus and so, and you lose.
I don't want to over play my hand on this. Sometimes that is a good thing. Many times I have read a book or done some other research, become convinced and then engaged a discussion. My interlocutor may ask questions that I can't answer because I can't recall the research at the time. In such a case it is not unreasonable for me to hold the line, though I may not be able to argue my case well.
Where I would go wrong though would be to dismiss my interlocutor's arguments without further investigation.
Also, there is the importance of reliance on credible authority, it is reasonable to do so. What I mean is that sometimes someone will argue a position I cannot refute, but I will maintain my position because a credible authority I rely on holds that position.
Again, this is reasonable to do so. But in the examples I just gave, reliance on past research or credible authority, there is a foundation for a position.
What I am arguing against, and what I think Tierney shows, is that often we take positions that don't have a good foundation, we just know heard someone say something their cousin told them after talking to a friend of an uncle who saw something on Oprah. Watch how easily "I heard so and so, or such and such" becomes a conversation stopper and you will see what I mean.