first, roi requires that all costs and benefits be stated in monetary units. because it is usually easier to quantify costs than benefits, roi measurements can be biased in a way that gives undue weight to costs. second, roi focuses on benefits that can be predicted. many electronic commerce initiatives have returned benefits that were not foreseen by their planners. the benefits developed after the initiatives were in place. another weakness of roi is that it tends to emphasize short-run benefits over long-run benefits. the mathematics of roi calculations do account for both correctly, but short-term benefits are easier to foresee, so they tend to get included in the roi calculations. long-term benefits are harder to imagine and quantify, so they tend to be included less often and less accurately in the roi calculation.