Realizing you are evil Good and evil, like most other things, are potentials.
When a being is developed with conditioning that make him good he is good, when conditioned to do evil, he is evil. Once you reach a certain age in development, maturity, you are by the states ruling, free to act on these potentials. As reason befits them, so they act.
Some people's goodness is stronger than their evil side, and visa versa.
There is also genetics to consider, but I am a philosopher not a geneticist. I can only claim that some people are more prone to act certain ways, behave, more or less towards moral degrees, because of their genetics. .
Having a Moral Sense is very important. Since most religions teach of doing good and being good, religious culture offers good people
To act for good in and of itself is another step up the chain of moral notation..