If you carry around a lot of suppressed or repressed anger (anger you have unconsciously buried) you may lash out at people, blaming or punishing them for something someone else did a long time ago. Because you were unwilling or unable to express how you felt in the past, you may overreact in the present, damaging a relationship.

The Nice Girl Syndrome: Stop Being Manipulated and Abused -- And Start Standing Up for Yourself