A manager has to make a set of decisions in his everyday life. This is the essence of the work of a manager. Generally, the manager will rely on intuition or experience to make decisions. In other cases, because of the complexity of the impact of his choices or because of a legal obligation, the manager will use different decision support system to guide him in his choices.

Among the most used tools, there is the weighting grid, where there are several criteria to evaluate, for which each of these criteria is weighted. The weighted average of these notes finally gives us a score allowing us to classify the different options. Unfortunately, the winner of this evaluation does not often match the one that the manager would have chosen using his intuition.

Although this method is widely used, it includes several mathematical biases which, when they are not well understood, could lead to erroneous solutions.

Another tool often used by the manager is the forecast. Many are trying to make forecasts of the future based on their understanding of the market, or based on history. Many are able to make forecasts, but few are able to give their predictions accuracy. The error associated with estimates allows the manager to assess the reliability of the results to which it relies for its decisions. A typical prediction method is the moving average. For example, in a simple situation where there are no seasons and no growth, the manager who would use the moving average to predict its stocks from the passed sales will be out of stock in 50% of the time.