There is power in having something to hold over another’s head. There is power in using a person’s weakness and failure against him or her. In moments when we want our own way, we pull out some wrong against us as our relational trump card.
Holding onto another's sin, weakness, and failure makes us feel superior to them. It allows us to believe that we are more righteous and mature than they are. We fall into the pattern of getting our sense of self not by the comfort and call of the gospel but by comparing ourselves to another. This pattern plays into the self-righteousness that is the struggle of every sinner.