Sometimes, one comes across some models which attempt to predict the behavior of a system based on past data. In order to come up with such models, the “outliers”, or data which deviate very far from the mean, are often left out.
However, it could so happen that in many systems, the entire behavior may be totally determined by the outliers. Also, it is difficult to choose an outlier and to understand how it could impact the system. So, much of the predictive modeling and “forecasting” turns out to be useless or even dangerous because they tend to mislead the human brain.