People often predict that they, and others, will be biased by sunk costs—they think that investing in an object or goal increases how much one values or wants it. In this article, we use sunk cost predictions to look at people’s theory of mind and their conceptions of mental life. More specifically, we ask which mental states and motivations are seen as underlying the bias. To investigate this, participants in two preregistered experiments predicted whether different kinds of agents would be biased by sunk costs, and also assessed the agents’ mental abilities. Participants predicted that some kinds of agents (e.g., human adults and children, robots) would show the sunk cost bias and that others would not (e.g., raccoons and human babies). These predictions were strongly related to the participants’ assessments of whether the different kinds of agents are capable of seeing actions as wasteful, but also related to their assessments of the agents’ capacities to feel regret and frustration.
