The belief in a supernatural source of evil is not necessary. Men alone are quite capable of every wickedness- Joseph Conrad

This quote is one of thoses sayings that is simple but true and deep. Anyone can look at this quote and right a way know what it means. It's not a riddle. It's saying that man is capable of all evil and there is no need for us to believe that there is a supernatural source of evil. Man is the source of evil. The supernatural might be real and this is not say that it doesn't exist but its says is that we should not believe that the supernatural is the source of evil. When bad things happen people often say that its the work of a demon or that some one is out to get them. Not all people say this but I know a lot who do. They blame it on things out side of our control.
A good ex:
In the movie the fourth kind, there is a lot of supernatural things happening. This is a movie base on a true story. In the movie the werid things range from: A little girl get kidnapped or abducted to someone who kills his whole entire family and blame it on what he saw. It goes as far as the main person in this movie psychologist Dr. Abigail records someone talking in a differecne language that little people understands and she herself say that she has been abducted herself.
I am not saying she was lying are its was all un ture because I think some of it might have been true. No one really knows. I think the part about the everyone seeing the owls is true and how they freaked out when they went under the spell( i don't know what it's called), but i believe that also is true because they have things were to show you. but the little girl being abducted and the man killing his whole family i do not think is from supernatural. I think the man killed his family because he went crazy not because some supernatural thing controled him. The little girl I do believe was killed and hinded by the mom to prove that it was true. I feel sorry for the mom because I do think that she believe that her child was abducted but again most likly she went crazy.

In the end it's what you believe in
but like in the story men are capable of all evil and there is no need to believe in the supernatural source of evil