(Proverbs 17:9 KJV) He that covereth a transgression seeketh love; but he that repeateth a matter separateth very friends.
A good way to ruin a friendship, poison a marriage or break up a family is to bring up some untouchable from the past. The first part of the verse implies that a wrong has been done. Whether it was resolved or allowed to fade from memory does not make any difference. It is in the past and should remain there.
A good way to ruin things is to bring it up again. It is always nice if people have confessed or the wrong was righted but it does not say that is necessary. Sometimes the scar has just faded in time and is best left to rest.
So? This probably goes with the admonition to be slow to speak that is given other places in scripture. As believers we are to leave the ugliness of the past in its grave.