Change consists of two characteristics: environmental and instilled behaviors, or beliefs. I feel confident in saying that people can successfully change who they are if they are changing environmental factors, assuming all variables are met. Environmental change is possible, through strong will, desire, and possibly the help of a counselor or therapist. However, instilled behaviors including beliefs, morals, and ethics are by far more challenging to achieve. Success in change of instilled behaviors may or may not be accomplished, I want to say more often not, and it takes a long time to achieve. Instilled behaviors, or learned behaviors, takes years of conditioning, from birth on, therefore, it would take years to reconditioning to change.
