When faced with a member of a disliked group who does not display the supposed negative characteristics of that group, someone may say, "oh well, he/she is one of the good ones." this is an example of: ?

This is an example of "Belief persistence".

The standard of belief persistence, expresses that 'While changing beliefs because of new proof, you should keep on believing however many of the old convictions as could be expected under the circumstances. Specifically, this implies if an individual gets new data, she needs to oblige it in her new belief set, and, if the new data isn't conflicting with the old belief set, at that point;(1) the individual needs to keep up every one of the beliefs she already had and (2) the change ought to be negligible as in each suggestion in the new belief set must be deducible from the association of the old belief set and the new data.