During World War II the U.S. submarine Tang surfaced under the cover of darkness to fire upon a large Japanese convoy off the coast of China. Since previous raids had left the American vessel with only eight torpedoes, the accuracy of every shot was absolutely essential. The first seven missiles were right on target; but when the eighth was launched, it suddenly deviated and headed right back at their own ship. The emergency alarm to submerge rang out, but it was too late. Within a matter of seconds the U.S. sub received a direct hit and sank almost instantly.
In much the same way we can destroy ourselves by hostility toward others. The effects of holding a grudge are very serious. Modern medicine has shown that emotions like bitterness and anger can cause problems such as headaches backaches, allergic disorders, ulcers, high blood pressure, and heart attacks, to name just a few. When we do not love our enemies but strike back at them, we are usurping God's prerogative to mete out justice. We read in the Bible, "Vengeance is mine; I will repay, saith the Lord!" By seeking revenge, we really inflict great harm on ourselves.