Two very important traits are hinted at here about our ability to see or hear the truth and pass along correct and accurate information. No one is with out fault, that is the nature of life, but one who determines a fault and fails to correct it is far worse off than the most ignorant of ignorant. If one is to associate with one not as good as your are then it is the responsibility of that person to convey the knowledge so the other can achieve greatness as well. This is the deshi-sensei relationship, the tori-uke, and the father-son, i.e. Yang and Yin.
The goal of the sage, one of them at least, is to not transfer anger and not repeat mistakes. Anger, emotions, the monkey brain, is that it does affect others with the speed of light and this saying points out to us that our responsibility is to achieve a level of practice to suppress our anger. Our anger is gone and that in itself allows the mind and spirit to actively listen and see truth. A sage errs and sees that as a means to learn and change so the error does not repeat itself. A lofty goal for the FMA to achieve in practice and training.