How does the presence of uncertainty affect the usefulness of the model?

Uncertainty within this simple one-dimensional model is very hard to ascertain. The linear nature of the profit to response rate belies the fact that other variables are not being considered. For example, if there is a low response rate, one may assume that little excitement for the product may generate smaller orders, thus profits may be far worse with a small response. Likewise, a large response rate may indicate lots of enthusiasm for the products and higher average orders. Some type of curved line would represent the relationship then between profits and response rate.