The sunk cost fallacy, which is the tendency to continue investing in a decision based on the cumulative prior investment rather than the current value or outcome, is targeted as a main reason why people, including Montell, stay in unhappy romantic partnerships.

Montell shares her experience of staying in a toxic, seven-year relationship with an older man she refers to as Mr. Backpack, a pseudonym she uses to protect his identity and avoid painful memories. They began dating when Montell was 18 and he was 29, initially connecting through playful texts that quickly escalated into a romantic relationship. After spending her college years traveling to Los Angeles to be with Mr. Backpack, she moved there with him, despite dreaming of living in New York. She excused Mr. Backpack and his increasingly manipulative and abusive behavior until she was 25, when she left him. Reflecting on the relationship years later, Montell now recognizes the influence of the sunk cost fallacy, realizing that she stayed in the relationship out of a fear of loss and a misplaced hope for future happiness.

Research suggests that the sunk cost fallacy has benefits— “it’s actually reasonable enough to want to continue a project based on the time and energy you’ve already spent on it” (59).