I am currently reading a book that was recommend by another poster about cognitive dissonance and why people defend bad choices called 'Mistakes were made(but not by me)'.
It explains why people only believe information that validates their choice, discounting information that does not. Not surprising, but what is interesting is the more people have invested in a decision, the more they think they were right and the less likely they were to believe they made a mistake, regardless of whether it actually was a good decision or not.
They gave the example of a doomsday cult, whose leader predicted the end of the world on a specific night. The leader believed she would be lifted into outer space along with her followers. Some waited with her at her home, some stayed at home to wait the end.
Many of her followers quit their jobs, gave away their homes, and dispersed their savings, waiting for the end. Who needs money in outer space? Others waited in fear or resignation in their homes. (Mrs. Keech’s own husband, a nonbeliever, went to bed early and slept soundly through the night as his wife and her followers prayed in the living room.) Festinger made his own prediction: The believers who had not made a strong commitment to the prophecy—who awaited the end of the world by themselves at home, hoping they weren’t going to die at midnight—would quietly lose their faith in Mrs. Keech. But those who had given away their possessions and were waiting with the others for the spaceship would increase their belief in her mystical abilities. In fact, they would now do everything they could to get others to join them.
That is exactly what happened. Despite the fact that the leader was completely wrong, her most ardent followers became even more dedicated to her. Big surprise, she suddenly had a new vision. The faith of the little group had spared the world from destruction. They became even more convinced of their belief and began proselytizing. Sound familiar? The Watchtower was wrong about 1914, but they simply came up with a new theory that the return of jesus was invisible and people believed, because they needed to believe. An impartial observer would see it for what it was, an excuse for failure, but they were not impartial, they needed it to be true.