The title of the book I read is FORGETTING YOUR PAST. It is written by BOB GASS.
The book actually focuse on Forgiveness. It taught me how dangerous it is to keep bitterness in my heart against someone else.
The book says and I quote;

Effects of Bitterness

• It will drag you down and turn you into someone that is merely existing
• It will cause you to leave a bad smell where you go, even to those that love you, they will get tired and leave you. This is because carrying bitterness in your heart is like when someone is carrying a corpse, no one will want to come close to that person.
• It will destroy every new relationship that God wants to bring into your life, because nobody will want to have and affair with someone who is having an affair with a corpse.
• It will destroy your health and shorten your life span, because God did not create you to carry bitterness.

There is a prison called Memory. Memory is the faculty that helps us relieve yesterday. You can be hurt everyday of your life, and if you take them off your mind and forget them, they can shorten your life span.