Freud proposed that the Id, which governs the need for immediate gratification, the Ego, which represents reason and rationalizes between the two extremes, and the Superego, which sets the standards, includes the conscience and is highly demanding within the value system, form the main three parts of the personality.
When there is not sufficient cross-section between these three and a child becomes fixated in one or the other, problems can manifest themselves in extreme behaviors.
Individuals governed by the Id may fail to recognize their selfish behavior and, with environmental factors at play, it is possible that inappropriate actions are not managed and individuals become mean and even evil. Sadistic tendencies are not unusual.
Physical manifestations of psychological origin can create neuroses and a psychosomatic disorder results. This can cause a person to become more neurotic and look for avenues to express himself. A fixated evil person will always look for physical reasons or environmental factors rather than look inward for psychological reasons for inappropriate behavior: externals are always to blame.
For the average person, the Ego and Superego will intercede long before the inappropriate behavior becomes completely uncontrollable or downright evil. Desire for power, a need for control and a right to freedom, when regulated by the Ego and Superego, can all be effective traits in a successful person.
The impulsive urges with which a child is born (the Id) can be unreasonable and represent the biological contibution to the psychoanalytical persepective. The Ego monitors and ensures satisfaction without the unreasonable and chaotic principles of the Id. As a child's world expands and environmental factors come into play, the Superego, consisting of the conscience and the ideal, combines to create a manageable and satisfying combination of good and evil tnednecies.
Unfortnately, the Superego sometimes places unreasonable expectations on the Id and guilt and inadequacies surface. In extreme circumstances, this can also lead to inappropriate behavior as feelings of failure manifest and a person tries to replace those feelings. The need and desire for power replace rational feelings and neuroses can surface only to be replaced by evil deeds as a person strives to substutute inadequacy with power.
From a psychoanalytical theoretical perspective, good will triumph over evil. However, biological factors and environmental issues can cause confusion and fixation and extreme behavior can result.