Shadow boxing, what Bill Wilson called a "searching and fearless moral inventory," is for the sake of truth and humility and generosity of spirit, not vengeance on the self or some kind of victory over the self. None of us need or expect perfect people around us, but we do want people who can be up front and honest about their mistakes and limitations and hopefully grow from them.
Apparently that's what God wants, too: simple honesty and humility. There is no other way to read Jesus' stories of the prodigal son (Luke 15:11-32) or the publican and the Pharisee (Luke 18:9-14). In each story, the one who did wrong ends up being right--simply because he is honest about it. How have we been able to miss that important point? I suspect it is because the ego wants to think well of itself and deny any shadow material within itself. Only the soul knows that we grow best in the shadowlands. We are blinded inside of either total light or total darkness, but "the light shines on inside the darkness, and it is a light that darkness cannot overcome" (John 1:5). In darkness we find and ever long for more light. I would call this dark grace. But most of us have only been taught about light and pretty grace, and so we miss at least half of our opportunities for encountering both God and ourselves." (Richard Rohr, Gateway to Silence)