There is only one way that evil can overcome a Christian, and that is if the Christian returns evil for evil. If someone insults you and snarls at you, you are not overcome. You are overcome if you begin to snarl right back. Then the unpleasant person has become your role model. You are copying evil and evil is overcoming you.
If someone hates you and you hate him back, then evil is getting the victory. If someone strikes you and you strike back, then you have become like the evil one.
The Bible says, “Do not be overcome by evil, but overcome evil with good” (Romans 12:21). If someone reviles you, you are to smile back and say, “God bless you.” The person will not know how to react to that, and you have overcome him. You have won. That person has not changed you, but you have gone on the offensive with the most powerful weapon in the world–love! If someone strikes you on the cheek, Jesus said you should turn the other cheek (see Matthew 5:39, Luke 6:29). And that will leave your adversary totally confused! And then on top of that you should say, “I love you.”
If someone forces you to go one mile, go two miles. If someone takes your coat, give him your shirt as well (see Matthew 5:40-41). Do so graciously, cheerfully, even assertively. God has given you the spiritual weapons to discern who your enemies are and then to conquer them by making them your friends. (Of course, as long as there are vicious criminals and international tyrants in the world, there must be a system of restraint through local or international police. In Romans 13, police and legitimate armies are considered by the apostle Paul as “ministers of God” to bring vengeance on lawbreakers.)