Unfortunately, marketers work with approximations. Underneath our stochastic sampling, and even embedded within our conversion heuristics, is an understanding that while the model seems rational, it is not. The cognitive calculus being conducted by the customer segment is always a matter of perception and not of reality. The customer is doing simple subtraction. They are subtracting total cost from total value, but they may have a completely unrealistic conception of either or both. The principle challenge of the marketer is to understand what the representative customer is truly thinking, and the representative customer is not a person; it is a composite. We are predicting the actions of a composite.