The self-destructive sin of bitterness
Are you tempted by bitterness? You need to repent. Bitterness is like eating rat poison and waiting for the other person to die. Giving into that sin does not harm your enemies, but it does harm you, emotionally, mentally and physically. It harms the people who love you and kills your chance at happiness.
Perhaps you were legitimately wronged. Perhaps something was taken from you unfairly, or perhaps you were denied a life goal that you legitimately deserved. Even if you are right, and you did unfairly lose something that is rightfully yours, the odds are you will never get that thing you so desire, which has become the god you worship. You need to let go of the loss and move on. If the people closest to you truly care about you, they have probably already staged an intervention. Listen to them.
But most importantly, those who embrace bitterness face the danger of eternal damnation in Hell fire. Jesus warns us in Matthew 6:14-15 that if we do not forgive, God will not forgive us. The sins that God has forgiven us are infinitely worse than anything anyone has done to us, because God is perfectly holy.
The most effective way to kill bitterness is to be thankful for God's blessings on our lives. Thanksgiving and bitterness are mutually exclusive. No matter what we have on earth, the infinite blessing of God sacrificing His only Son as payment for our sins against Him is more than enough reason for joy. If you are a bitter person, repent. Our Father in Heaven loves you and does not want you to live the life you are living. Accept Jesus Christ, and learn true forgiveness.