It's funny how the mind can get used to practically anything. Specifically in terms of the environment it finds itself in. There are people who live in extreme cold, and others who live in extremely hot environments. But no matter how tough living in such places is, the brain always ends up getting used to it. That also goes for darkness. Most people are used to being out in the light, surrounded by the people they know and love, however, that isn't the case for everyone.
There are people who are so used to resentment and abuse that they'll retract into the deepest, darkest corners of the world, even though it scares them. However, as years go by they'll learn to live with it. They adapt to their new reality, and it turns them cold. There are many reasons to find your way to dishonor and darkness, but like many other things there is a most common way for that to happen. Betrayal, the act of shattering the reality of another.
Betrayal breeds distrust, which in turn breeds darkness. Darkness leads to despair, and despair leads to desperation for connection to other people. In most cases, this will be a phase, but what applies to everyone is the lingering fear of being betrayed again. A fear that may leave its victim unable to bond with others ever again. But for such people, there is a way to return to life, so to speak. To overcome their fear by facing it over and over again, until they're left without the ability, nor the need to depend on others. These are the people who cause wars, death, and destruction.
These are the people who forces mankind to progress, however, the uneducated and the stupid fail to appreciate this phenomenon, branding it 'evil' rather than recognizing it for being the great driving force behind technological progress....