Why do Good People do Bad Things?

“You either die a hero, or you live long enough to see yourself become a villain.”- Harvey Dent a.k.a Two-Face
Every day of our waking lives, we are a witness to the eternal battle between good and evil. As for my own principle, an action can be considered good is if the deed is not harmful to both parties, and vice versa. From this standpoint, we can narrow down the answer in two main reasons why good people do bad things.
Firstly, it is dependent on the intellectual capability of a person. Ignorance is one of the driving reason for people to do harmful things. Sometimes, a man can do an action without evaluating the possible consequences and lack of awareness about options can force people to do things that are damaging to others. One example for this is obedience for authority. You can be deceived by instructions from a person with power to do things and leave behind the responsibilities for your act, resulting to harm other people. A related scenario is about the Holocaust that had happened in Nazi era in Germany during the WWII.
Secondly, it is dependent on the emotional capability of a person. Emotions is one variable of making decisions. Burst of emotions can cloud out the rational thinking of a person an can commit acts which can be uncontrolled. One scenario is when a person, with a very limited financial capability, has a family member in a hospital that needs immediate operation, chances are, this person can succumb in the temptation to steal of even kill another person in exchange of money. Even if there is a good reason behind a bad deed, still, other person/s are harmed in the process of how he decided to solve the situation.
The scope of my essay is on an average thinking person who can learn and become educated further. An exception to this, in my opinion, are those people who are mentally handicapped, simply because they cannot comprehend the consequences of their actions and they are incapable of distinguishing right from wrong.
There are other answers for this essay that has not been discussed because I am and amateur MBA student with limited knowledge about psychology and philosophy. However, the shorter answer for the question “Why do Good People do Bad Things?” is on the quote below.
“In each of us, two natures are at war – the good and the evil. All our lives the fight goes on between them, and one of them must conquer. But in our own hands lies the power to choose – what we want most to be we are.”
― Robert Louis Stevenson