Proverbs 18:19 A brother offended is harder to be won than a strong city: and their contentions are like the bars of a castle. 

This means that when a close relationship, like that between brothers, is broken by offence or betrayal, it is extremely difficult to repair. Winning back that trust can be more challenging than conquering a fortified city. The hurt and bitterness can build walls around the heart, just as strong as iron bars in a castle.

A brother offended by wrong dealing is harder to reconcile than taking a strong city, but brothers who stand united are stronger than a castle.

When trust is violated, especially by someone close, the wound cuts deep. Rebuilding that trust takes great effort, patience, and humility. But on the other hand, when brothers, or close companions, stand together in loyalty and love, their unity becomes a powerful defence. Just as a castle is hard to breach with its thick walls and bars, so is the bond of unity, unbreakable and resilient against outside threats.