confirmation bias
"
It is the peculiar and perpetual error of the human understanding to be more moved and excited by affirmatives than by negatives." --
Francis Bacon (True, as long the affirmatives support your beliefs about anything but yourself or people you don't like and the negatives oppose your beliefs about anything but yourself or people you don't like. When it comes to the self or people we don't like, we seem to be much more affected by negative views than positive views. See the entry on
negativity bias.)
Confirmation bias refers to a type of
selective thinking whereby one tends to notice and to look for what confirms one's beliefs, and to ignore, not look for, or undervalue the relevance of what contradicts one's beliefs. For example, if you believe that during a full moon there is an increase in admissions to the emergency room where you work, you will take notice of admissions during a full moon, but be inattentive to the moon when admissions occur during other nights of the month. A tendency to do this over time unjustifiably strengthens your belief in the relationship between the full moon and accidents and other
lunar effects.
This tendency to give more attention and weight to data that support our
beliefs than we do to contrary data is especially pernicious when our beliefs are little more than prejudices. If our beliefs are firmly established on solid evidence and valid confirmatory experiments, the tendency to give more attention and weight to data that fit with our beliefs should not lead us astray as a rule. Of course, if we become blinded to evidence truly refuting a favored hypothesis, we have crossed the line from reasonableness to closed-mindedness.