In an article entitled, Bias for Confirmation, we find this useful little tidbit:
In an experiment, people were asked to determine the length of a line. One group was told to decide how long the lines were in their heads; another group was told to write it on a Magic Pad (pads for children that erase what you write when you lift up the top sheet) and then erase it before anyone saw it; and a third group was told to write their conclusions on a piece of paper, sign it, and give it to the researcher.
Then the subjects were given information indicating their first conclusion was wrong, and they were given an opportunity to change their decision. Those who decided in their heads changed their conclusions the easiest; those who wrote it on the Magic Pad were more reluctant to change their minds; and those who declared their conclusions publicly remained most convinced their first conclusion was correct.
Their feeling of certainty was an illusion; it wasn’t related to their conclusion’s accuracy. It was being influenced by another factor — how publicly they had made their conclusions.