Fill in the empty space appropriately.

1) Ignoring the phenomenon, and thus not assigning any values to the parameters that represent it, may very well generate less controversy than assigning them questionable values. It is sometimes not obvious whether a certain detail can be ignored or not. A model, being an abstraction, will always involve ignoring certain aspects of the real world. Many of these omissions are obviously harmless, but some are not. The ............................... sometimes makes us forget that there ever was an issue, and that is the danger.

2) Thera are three principals of Operations Research that should be obeyed in all studies. "Scientific Approach" and "System Approach" are two of those principals. The third principal is "................................................ Approach".