The one who was hurt may have trust issues with the one who did the injuring. In other words, this could be the 25th incident of hurt. Try to discern how often the person has been hurt by the other. If there is a pattern, then it is understandable why the injured person is hesitant to reconcile.
In this kind of case, I recommend being aware of small steps, done by the injuring person, to truly change and be trustworthy. If the one who acted unfairly does not characteristically engage in hurtful actions, then perhaps there is a trust issue (in the one who refuses to forgive) that goes back a long way, even to childhood. Those who are mistreated by parents, for example, have difficulty establishing trust in their later relationships with others. If this is the case, then practicing forgiving of parents may help the person to more easily trust people in the present and move toward a healthy reconciliation.