Given the plethora of available information systems (IS) evaluation techniques, it seems unlikely that yet another technique will address the problems of unsuccessful projects and ineffective management. Rather, more insight into the foundations of evaluation techniques may yield greater benefits. One generally accepted, but largely unexplored, issue concerns objectivity and subjectivity in the assessment of costs and benefits. This research in progress demonstrates that, over time, the objectivity of evaluation approaches has diminished as they increasingly assess benefits. As cost measurements remain more objective, assessments that seek to compare costs and benefits become more problematic; benefits are from Venus, costs are from Mars and their orbits are diverging. This research assesses why this is the case. Specifically, it examines different characteristics of costs and benefits and the divergence in their assessments. Then, a design science methodology is adopted to analyse the divergence’s influence on evaluation methods, as well as the 'tweakability’ for closing the gap. In this paper it is argued that narrowing the gap, and particularly the objective measurement of IT benefits, is a prerequisite for a more general acceptance of IT evaluation methods. This insight may enable better understanding of some of the fundamental problems underlying IS evaluation.