Allow to to start by saying I enjoyed this post and think Yvain makes an interesting point. It may help explain why rumor spreads well. I have however one difference of opinion, which is that if a person adds “I arrived at this belief through evidence”, I would believe their statement more. I would assume they are talking about a non-Bayesian, layman’s version of “evidence.” (If they’re talking about Bayesian evidence, they’re probably Bayesian and this is also a mark in their favor)
For instance, in mathematics it’s common to state that something is true, and add “And we can prove this.” It’s often too much work, or beyond the scope of the course, or beyond the mathematical abilities of the class, to actually look at the proof.
I often arrive at opinions by asking others’ their opinion. I do not want to spend the time to evaluate the evidence on global warming, for example. I simply trust that friends and experts I know to be well-informed know what they are talking about when they say a trend exists. But, I you know me to be rational in evaluating arguments and a careful reader, and you do not trust my unknown friends as much, you should trust what I say more if I indicate I arrived at it through firsthand evidence, than though the opinions of my friends. You may want to trust firsthand evidence more regardless, because content and thus authority is lost at every telling.
This might be one reason urban rumors in particular spread so much better; they’re typically told as though they happened to the teller or a close friend of the teller.
My mother made this argument to me probably when I was in high school. Given my position as past infanticide candidate, it was an odd conversation. For the record, she was willing to go up to two or six years old, I think.
And let us not forget the Scrubs episode she also agreed with: “Having a baby is like getting a dog that slowly learns to talk.”