Mental process that removes unacceptable thoughts and memori…

Mental process that removes unacceptable thoughts and memories from consciousness and keeps them the unconscious.    For example, a veteran goes through a traumatic experience during the war and while in therapy, the psychologist notices that this memory has been “blacked out” for the veteran. He can not recall the day of the incident at all (likely because it was so traumatic and uncomfortable).    What is responsible for this?