Psychologist Leon Festinger: 
A man with a conviction is a hard man to change. Tell him you disagree and he turns away. Show him facts or figures and he questions your sources. Appeal to logic and he fails to see your point.
From the Science of Why We Don't Believe Science (via Daring Fireball).  I'm definitely guilty of being unwilling to accept information that doesn't agree with my beliefs, and I feel kinda bad about that. #science