It is unavoidable that empirical models are misspecified in various ways, but adopted empirical methodologies rarely address this. This column focuses on the misspecification of exogenous structural disturbances which are the forces that drive fluctuations in modern business cycle models. It shows that the conclusions drawn from estimated models can be severely distorted if structural disturbances enter the model in an incorrect way, even if the misspecification is minor. It proposes the novel concept of an agnostic structural disturbance, which can be used to detect and correct for misspecification of structural disturbances. While agnostic in nature, studying how ASDs affect model properties enables us to give them an economic interpretation.