Predicting individual differences in placebo responding has proved hard. Predictions from dispositional or personality variables are unreliable for two reasons: first, because dispositional predictions fail to account for situational variability, and second, because the dimensions identified in popular dispositional models are inter-individual variables, and may not map on to intra-individual structures and processes involved in placebo effects. This thesis describes a new psychological mechanism of placebo responding—motivational concordance—which links placebos with established research on human values and goal striving.