To a great extent, the successes or failures that a person experiences in life depend on the decisions that he or she makes. One decision may make the difference between a successful career and an unsuccessful one. What makes the difference between good and bad decision ? A good decision is one that is based on logic, considers all available data and possible alternatives, and applies the quantitative approach we are about to describes. Occasionally, a good decision results is an unexpected or unfavourable outcome. But if it is made properly, it is still a good decision. A bad decision is one that not based on logic, does not use all available information, does not consider all alternatives, and does not employ appropriate quantitative technique. If you make a bad decision but are lucky and a favourable outcome occurs, you have still made a bad decision. Although occasionally good decision yield had results, in the long run, using decision theory will result in successful outcomes.