If there is a lot of built up psychological stake in a certain position or attitude and a piece of solid evidence comes in which conflicts with that position, it may be easier, psychologically, to dismiss the new information than alter the existing structure.
You can imagine how ingrained psychological structures can be when a human being is raised within a certain country, system, or reality. Growing up in the US, or any culture, for that matter, you will absorb an overwhelming number of messages about what is true, what is possible, and what is important.
Many of of these messages are absorbed subconsciously and become part of the basic structure of our reality. It becomes very difficult to question the fundamentals when opposing messages only come in small doses from the “fringe.”
Consider these two examples:
Believing that your friend is trustworthy (having built up that attitude over years of experience) is a cognition that would be dissonant with the sudden discovery of your friend stealing money from you. As a result, you might seek to dismiss or minimize the importance of this new information—maybe telling yourself it was a freak thing, a joke, or an accident, or that he was broke or desperate or on drugs. You might even try to forget that you saw it.
In presenting new, contradictory (dissonant) evidence concerning 9/11, it is frustrating how many people immediately begin to bring up rationalizations and excuses in order to dismiss the significance of the information. You can often witness cognitive dissonance in action as these skeptics try to avoid the psychological turmoil of facing the very disturbing implications of 9/11 Truth. The collapse of WTC 7 is an interesting example. Skeptics are likely to quickly dismiss this piece of evidence rather than acknowledge the suspicious fact that the destruction of a third skyscraper was essentially blacked-out of the official story of 9/11 by the government and media.
“Conspiracy theories” seem to be the quintessentially cognitive dissonant concepts of our culture. For many people, the idea that JFK was killed by the government or “9/11 was an inside job” threatens the entire fabric of their consciousness. These things simply cannot be true and people will bend over backwards and resort to irrationality and ridicule to avoid considering them.
Cognitive dissonance can work both ways. It is extremely difficult to maintain a vigilantly open mind. Whatever your dominant perspective or worldview happens to be, it is inevitable that you will sometimes use rationalizations in order to save the time or mental stress of dealing with conflicting information. Cognitive dissonance is actually a necessary and natural mental function, but it is also a phenomenon that we should be aware of, in ourselves and others, as it is a process that does not always serve us well in the quest for objectivity and truth.