Ephesians 4:26-27 (NLT)
26 And �don�t sin by letting anger control you.� Don�t let the sun go down while you are still angry, 27 for anger gives a foothold to the devil.

Anger is defined as a strong feeling of annoyance, displeasure, or hostility. The apostle tells us not to allow anger to control us for it opens a door of opportunities for the devil to take advantage of.

In June of 2012, Carl Ericsson, a 73-year-old South Dakota man, was sentenced to life in prison after admitting to the murder of a former high school classmate. Friends and family members were shocked that the once-successful insurance salesman seemed to snap. Ericsson had been married to his wife for over 44 years.

But after the murder, Ericsson's secret finally came out. For over 50 years he had simmered with a belated grudge: He was still mad about a classmate who had once pulled a jock strap over his head during a high school locker room prank. Norman Johnson, the classmate and murder victim, was a star athlete on the track team. Ericsson was a student sports manager. According to Ericsson's confession, on one occasion Johnson put a jock strap on Ericsson's head, humiliating him and planting the seed of resentment that would continue to grow for over half a century. Apparently, throughout their lives, Norman Johnson continued to outshine Ericsson. Prior to his murder, Johnson had competed in college football, earned a degree, and then taught and coached at his alma mater for more than three decades.

After holding the grudge for over 50 years, Carl Ericsson rang Johnson's doorbell and shot him dead. Ericsson told a judge, "I guess it was from something that happened over 50 years ago. It was apparently in my subconscious." During his sentencing, Ericsson turned to Johnson's widow and apologized, saying, "I just wish I could turn the calendar back." [Matt Woodley, managing editor, PreachingToday.com; source: Cameron Smith, Bizarre S.D. murder caused by resentment over 50-year-old locker room jockstrap prank," Yahoo Sports Prep Rally blog (6-18-12)]

Anger is an unusual emotion. It doesn�t just develop on its own, but is usually the result of another emotion that came first. In the story above we see the man was humiliated and then he felt resentment and then it finally boiled over to anger. It is why we are told not to let anger control us; for it will force us into doing things we may not have done.