The specific fault identified in these two proverbs is the piece of dishonest reasoning that takes place when a person attempts to justify revenge by trumped up charges against another. He deliberately perverts his faculty of judgment to find fault when there is no significant fault.
Strict honesty is required in all dealings among the Lord’s people. We are to be as honest with others as we are with ourselves. Just as we excuse minor misdemeanours that we see in ourselves, we are to overlook the same in others and not to impose another standard on them, since this is not to love our neighbour as ourselves. Do we hear that someone has said something critical of us? Well then, we do not simply respond in kind, upping the temperature by reporting some alleged misdemeanour with fictitious details added. This is the basis of all gossip which is the opposite of the spirit that should exist in the church of Christ.