Then the Lord said to Cain, “Why are you angry? Why is your face downcast? If you do what is right, will you not be accepted? But if you do not do what is right, sin is crouching at your door; it desires to have you, but you must rule over it.” - Gen. 4:6-7
We fool ourselves by thinking that we can master sin. We tell ourselves that sin doesn't really exist, or that good people like us who are well-intentioned can't really sin seriously.
But everyone I've known who thought they could master sin ended up mastered by sin. Myself included.
Sin indeed is crouching at our door, desiring to have us. Perhaps this intentional aspect of evil is proof of the malevolent angels, the devil and his demons. There is certainly a scheme that we fall into when we sin, and the scheme is not our own. It is a scheme that even out-schemes the schemers. Even at our most malevolent, we are no match for the malevolence that engulfs us and entraps us as we do wrong to others.
In the Pope's latest encyclical, he talks again about how "goodness comes from God" (Par. 19).
Once I think that by turning away from God I will find myself, my life begins to fall apart ...
This is true psychologically, practically, spiritually. This is true on every level. But we keep ignoring this lesson.
Perhaps the greatest barrier to evangelization these days is our sense of self-sufficiency. We're just fine, thank you, while we do horrible things to one another for the best of reasons and wake up one day and find ourselves in hell.
Jesus said ...
Apart from me you can do nothing. - John 15:5
He could have added, "except a lot of harm."