It doesn't matter how long we have held on to anger, lack of forgiveness, self-hatred, pity, resentment, ungratefulness, etc., etc. We can change our thought patterns and change our lives. We are what we choose to be. When someone hurts us, we react and we don't forgive. We hold on the hurt.
Nobody really cares.
We are choosing what we are to become. We go where our thoughts take us. I remember one client who had experienced a medical condition for almost 20 years. She changed her diet completely, exercised everyday, and spent time each afternoon receiving the healing benefits of sunshine. This client was carrying around 20 years worth of anger and bitterness towards her deceased mother.