One simplifying assumption in inventory modeling is that demand is known and constant. this means that probability distributions are not needed and it allows us to build simple, easy-to-understand models. Demand, however, is rarely known and constant, so the model we build lacks some reality. Introducing probability distributions provides more realism but may put comprehension beyond all but the most mathematically sophisticated managers. One approach is the quantitative analyst to start with the simple model and make sure that it is completely understood. Later, more complex models can be introduced slowly as managers gain more confidence in using the new approach. Explaining the impact of the more sophisticated models (e.g. carrying extra inventory called safety stock) without going into complete mathematical details is sometimes helpful. Managers can understand and identify with this concept, even if the specific mathematics used to find the appropriate quantity of safety stock is not totally understood