The sunk cost effect is defined as an increased tendency to continue investing in an endeavor once a previous amount of money, effort, or time has been expended. The current experiments attempted to identify individual differences, as well as situational factors that affect this decision bias. A theoretical model was proposed, and support was found for the existence of two constructs related to the ultimate choice to re-invest. Participants’ ratings of the potential success of the project were strongly related to their decision to continue the endeavor, while their ratings of responsibility for the initial choice had a smaller, yet significant relationship with the investment rating. Variables contributing to these constructs were also investigated. Mixed results were found for the existence of individual differences among decision-makers in sunk cost decision tasks.