None of us has endured evil as Jesus did. He goes to the parties, tries the drugs, and experiments with sex. It's tough for us to do this for the good of our fellow Christians, let alone for our enemies.
It is possible to let the wounds of your life define you so you lose your confidence, peace, and joy. This does not always occur, but as we saw in Romanspeople who have done wrong are often shamed when we do not repay them in kind, and they stop mistreating us.
Difficult or not, Paul is calling us to live as Jesus did. The infliction of vengeance is not a sign of strength, but of weakness. Cynicism is rife.
To repress the desire for revenge is to gain a victory over self, which is not only nobler in itself, but will also be much more effectual. Now Paul comes to the final command of the chapter. Evil struggles to stand against courageous and sacrificial love.