Apparently 666 is an evil number - something about the devil.
If you ask me, which I deduct you are since you're reading this post, the concepts of evil and the devil as the embodiment of evil are just part of the fairytale of the life of humans. You see, we've made up all these stories that explain how we're not actually responsible for our actions. So, we can easily blame away some heinous thing we did by blaming it on the devil, or maybe the "evil part of our nature".
This is the dictionary definition of the word evil:
profound immorality, wickedness, and depravity, especially when regarded as a supernatural force.
The only evil in this world that I have seen in my life is in people. Not once have I seen evidence of supernatural influences. All there is to it is that some people have little to no consideration for the lives and experiences of others - be they human, animal or plant. It's safe to say that every single person has lacked consideration for another at least once in their lives.
To be fair, consideration is not something that comes naturally to most people. Everyone may have moments of thinking about others first, but in a way consideration is a skill that must be practiced - and this only happens when one consciously and deliberately takes points outside oneself into consideration.
Look around you - it can easily be argued that every single issue in society is at least partly because of a lack of consideration - not simply from one party, but from everyone. We cannot simply blame the government for not providing adequate education or healthcare structures as if we are innocent bystanders in the matter. The people most likely to stand up and try to change something are the ones who are directly affected by it - and the reality within this is that very often the people who are most commonly affected by truly unpleasant life circumstances are the people who do not have the skills, power or knowledge to do anything about it. People in positions of "power" are less likely to experience the unpleasantness first-hand and are therefore less likely to care enough to initiate effective action.
And then... there are those who exploit, manipulate and downright abuse whatever is in their path in order to gain power (power in this case includes position, money etc). This can be seen all over the world in pretty much every single major industry. The producers of palm oil devastate natural habitats and murder the inhabitants of those ecosystems in order to produce palm oil. Not only that, but the lack of consideration trickles down and seems to affect the employees as well, who, being forced into a position of doing or allowing horrible things to survive, will then start committing horrible things themselves, such as setting a tree on fire that has an orangutang in it because they are clearing the area to plant even more palm trees.
Consider the position of poachers - unable to earn decent money elsewhere without skills or an education, some people turn to killing wildlife in order to sell the valuable body parts. This may not be something they want to do, so what some do to block out the horror of their actions is to simply stop caring.
In a sense, most people who contribute to our broken society (most of them being low income earners) do not have much choice in terms of their work - they do what they must to survive. The other part of the equation is that there are only a handful of people in the world who care enough to stand up and say that what we do is unacceptable, that the way we live is unacceptable. Most people simply accept these things as facts of life that cannot be changed. This unwillingness to participate in investigating the causes of issues in society, develop holistic solutions and actually stand up for change is the true evil in the world. Every single one of us knows that how we live is morally wrong, and yet true corrective action is rare.