There is growing interest in whether and how sunk-cost effects for purely behavioral investments occur. In this article, we further discuss Cunha and Caldieraro’s (2009) Behavioral Investment Sunk Cost (BISC) model and reconcile Otto’s (2010) results with the BISC model predictions. We also report new data from two unpublished experiments that are consistent with the BISC model, and we discuss the conditions under which purely behavioral sunk-cost effects are likely to be observed.