can people really change?

i had a professor in college who used to say that people don't change, not even from religion. at the time i didn't realize what he meant. now i do. people can change certain behaviors within themselves but one can't change ones essence. one can channel ones anger in a positive fashion and not give in to ones gut reactions. but they are still there under the surface. a shy person can force their self to be more social, but innately their first gut reaction will be to be shy. an overly sensitive person will always have such sensitivities even  though they may be able to rationally confront a stressful situation. ones core make up is g-d given. what we do  have control over is how we channel these attributes.