The Elusive Technology ROI

Why is it so hard to measure the ROI on technology? How might we make some sense of the controversy surrounding IT's value? Should we let our vendors tell us what the ROI of a new technology might be at our company? Do we have all of the facts to make a legitimate prediction of ROI prior to undertaking a project, or does the ROI analysis require making a lot of "glass-half-full" conjectures? Information systems managers continually struggle to evaluate potential projects and establish the bottom-line effect of IT investments. There must be an easier way to perform this important task.