Confirmation bias

Confirmation bias is a type of selective, wishful thinking, and an example of cognitive dissonance, where a person searches for or interprets evidence or information that matches their existing beliefs or predictions and ignores information that contradicts this. In short: cherry picking your evidence to match your conclusion. It is at the root of many types of pseudoscience and pseudohistory. The technique of cold reading, combined with the Forer effect, is an example of how a person may use someone's confirmation bias - a person who goes to a psychic or spiritualist session is going to want, often desperately, to hear from their deceased friends and relatives, and are quite willing to suspend their disbelief and ignore mistakes because of the emotional importance the 'hits' have.

The current segmentation of political thought and opinion brought about by the popularity of political blogging has caused concern for some in that it allows people to feed their own confirmation biases a lot easier - a person can read a blog which mirrors their own ideology and beliefs and not be subjected to any differing views or evidence that doesn't support the ideological line.