From the 19 September 2011 article at Science News Daily

The main reason that misinformation is sticky, according to the researchers, is that rejecting information actually requires cognitive effort. Weighing the plausibility and the source of a message is cognitively more difficult than simply accepting that the message is true — it requires additional motivational and cognitive resources. If the topic isn’t very important to you or you have other things on your mind, misinformation is more likely to take hold.

And when we do take the time to thoughtfully evaluate incoming information, there are only a few features that we are likely to pay attention to: Does the information fit with other things I believe in? Does it make a coherent story with what I already know? Does it come from a credible source? Do others believe it?

Misinformation is especially sticky when it conforms to our preexisting political, religious, or social point of view. Because of this, ideology and personal worldviews can be especially difficult obstacles to overcome.

Even worse, efforts to retract misinformation often backfire, paradoxically amplifying the effect of the erroneous belief.

“This persistence of misinformation has fairly alarming implications in a democracy because people may base decisions on information that, at some level, they know to be false,” says Lewandowsky….

…

In their report, Lewandowsky and colleagues offer some strategies for setting the record straight.