"To take revenge halfheartedly is to court disaster; either condemn or crown your hatred"

This quote by Pierre Corneille is a caution against retaliating in a halfhearted manner. He is recommending that if you are going to retaliate, you need to do it with complete commitment and conviction. If you are not willing to do this, then it is much better to not take revenge at all. He is suggesting that if you are going to retaliate, you should do it with full force and not hold back. If you do refrain from doing this, then you will be inviting catastrophe. He is also recommending that if you are going to retaliate, you need to either fully condemn the individual you are taking revenge against or fully crown them with your hatred. In other words, you must either entirely dislike them or completely forgive them. Retaliating halfheartedly will only cause catastrophe.