People who write their opinion publicly tend to stick to them despite contrary evidence. This is the finding of social psychologists Morton Deutsch and Harold Gerard, as described by Robert B. Cialdini in his book Influence: The Psychology of Persuasion.

Deutsch and Gerard conducted an experiment. They showed lines to three groups of college students and asked them to guess the length of the lines.

1. They instructed the first group to write down their estimates, to sign their names to them, and to give these to the experimenters.
2. They told the second group to write their estimates on a Magic Writing Pad and to erase them afterwards.
3. Then they asked the third group not to write anything.
   
   

Later, these groups “were given new evidence suggesting that their initial estimates were wrong, and they were then given the chance to change their estimates."

Deutch and Gerald discovered that “by far, it was the students who had publicly recorded their initial positions who most resolutely refused to shift from those positions later.” The second group also resisted, but members of the first group were malleable. Cialdini observed: “The students who had never written down their first choices were the least loyal to these choices. When new evidence was presented that questioned the wisdom of decisions that had never left their heads, these students were the most influenced by the new information to change what they had viewed as the ‘correct’ decision.’”

I find the result of this experiment happening every day in cyberspace. Once we have written down our opinions in Facebook we tend to resist contrary evidence. The more the other party presents data to us, the deeper we dig into our foxholes. Unless we are open-minded, we’re stuck.

This resistance has another explanation. Years ago when email was new, I bought a 1996 copy of The American Heritage Book of English Usage: