Do the right thing: The assumption of optimality in lay decision theory and causal judgment

•We investigated lay theories of decision-making.•The quality of rejected decision options is used in assigning causal responsibility.•Lay decision theorists hold an optimality theory of decision-making.•The global optimality of the agent and the local optimality for the goal are used.•These results inform theories of social cognition and of strategic interaction. Human decision-making is often characterized as irrational and suboptimal. Here we ask whether people nonetheless assume optimal choices from other decision-makers: Are people intuitive classical economists? In seven experiments, we show that an agent’s perceived optimality in choice affects attributions of responsibility and causation for the outcomes of their actions. We use this paradigm to examine several issues in lay decision theory, including how responsibility judgments depend on the efficacy of the agent’s actual and counterfactual choices (Experiments 1–3), individual differences in responsibility assignment strategies (Experiment 4), and how people conceptualize decisions involving trade-offs among multiple goals (Experiments 5–6). We also find similar results using everyday decision problems (Experiment 7). Taken together, these experiments show that attributions of responsibility depend not only on what decision-makers do, but also on the quality of the options they choose not to take.