The American Psychological Association ranked Leon Festinger the 5th most influential psychologist of the 20th century.
I was taken by his quote, "A person with conviction is a hard person
to change. Tell him you disagree and he turns away. Show her facts or
figures and she questions your sources. Appeal to logic and he fails to
see your point."
Changing anyone is difficult but there are mitigators. I list five in my PsychologyToday.com article today.