It's the natural tendency for people to interpret evidence in the way that supports their prejudice. Go to any football match (I'm thinking soccer as I'm a Brit, but I guess USian football is probably the same) and ask two supporters from different sides what they honestly thought of the merits of a referee's decision. 90% of the time they will agree with decisions that went their way and disagree with decisions that went the other way.
My mum watches a load of those "psychic detectives" TV programmes, and whenever I watch one with her, I steadfastly refuse to accept as credible anything I'm seeing. Why? Because I don't believe in psychic powers. All that evidence, all those police officers saying they would never have solved the case without the psychic's help, I disregard it out of hand. I don't know why it's invalid, I can't prove that any of them are lying and I don't have the statistics to hand about how often "psychics" turn out to be time-wasting frauds that get in the way of investigations, I don't care. I've made my mind up and I ignore any evidence that I am presented with. I guess I'm just as bad as AGW-deniers.