Good and evil are not difficult to grasp. Good creates and maintains order. It protects the bigger picture through a systemic view of the universe. A heroic man knows that his life is more than singular. He is an interactive part of something larger, so he identifies with more. He scales his influence through the principles that define him.
A good man handcrafts his values, communing with others who share his goals. Self-sacrifice comes naturally for a hero because he knows he is not losing himself when he invests his life into something authentically greater. Men can only be truly good when they have struggled to find their principles and carry them out in the world.
Evil is far easier to adopt as the primary motivator of your actions. Darkness is short-sighted, for it thinks only of its immediate needs. Instant gratification consumes an evil mind. Villains grow apathetic to the long-term effects of their actions or subjective experiences of other people. They sacrifice the larger order for immediate gain.
You might think you know what you are building towards, but doubts will enter your mind along the way. You will be tempted, again and again, to ignore the big picture of your goals and let shallow greed divert you. Lust appears for any of the basic pleasures in life, turning something beneficial into a vice. Beware your momentary urges, for they can betray you.
However, denying your darkness can never cure you of its influence. Denial only temporarily pushes it away. The way to neutralize its harm is to understand it completely. You must reach a level of intimacy with yourself such that no stone of your personality is left unsearched, no matter what you find beneath. Then you and darkness can co-exist.
Every superficially good person is frightened by their capacity for evil, limiting their ability to act. They must safely explore their darkness within the mind, where no physical damage can occur. A dark idea only becomes dangerous when its consequences affect others. Contain them so you learn about them.
Whatever you cannot explore in your imagination is something that still holds power over you. For a sufficiently powerful mind, no concept is forbidden. Murder, rape, and the wanton destruction of property can freely occur there. Ask if you are strong enough to keep your dark impulses where they can do no harm.
Can your actions remain virtuous while your mind wanders to forbidden territories? If you hide the part of yourself that preys on powerful urges, you will eventually falter and create destructive consequences. Master the dark part of yourself while you are young and can manage the temptation of dark actions, or else it will sprout like weeds in a garden.
A hero is neither his garden nor the weeds within, but a flourishing jungle of many acres. There is a natural balance to the ecosystem within. In that natural ecology is where you will find harmony between your darkness and light. There, you will choose what kind of character you are going to be: good or bad, heroic or villainous. Then you will change the world.