If you want people to believe you - you must speak first.

Research tells us that we tend to believe the first thing that we hear about a subject, whether or not it is true.  It's part of the primacy effect. 

Then, once we believe something, we use selective perception to hear only new information that supports our beliefs, while blocking out additional information that does not. 

We do this to deal with the upset, known as cognitive dissonance, that occurs when we have a conflict between what we believe to be true and new information. 

Since cognitive dissonance creates such an uncomfortable feeling, we opt instead for denial.  How could something be true when it makes us feel bad?  Better to just ignore it and pretend. ( McLeod, 2014)

It makes perfect sense, but it does provide a significant challenge for people trying to change perceptions.

Consider Paul McCartney, who on October 22, 1969 appeared on the BBC to refute three years of rumors about his death.  He did so by paraphrasing a comment made by Mark Twain in 1897 when he faced a similar situation, saying: "The rumors of my death have been greatly exaggerated." 

Sadly, not everyone believed him. (Early, 2017)

McLeod, S. (2014) Cognitive Dissonance simplypsychology.org.  Retrieved January 17, 2018, from

https://www.simplypsychology.org/cognitive-dissonance.html

Early, C. (2017, May 12) October 22, 1969: Beatle Paul McCartney denies rumours of his own death. bt.com  Retrieved January 17, 2018, from

http://home.bt.com/news/on-this-day/october-22-1969-mccartney-speaks-out-about-the-paul-is-dead-rumours-11364011642388