Purpose Monitoring of client progress in psychological therapy using formal outcome measures at each session has been shown to increase the effectiveness of treatment. It seems likely that this ‘feedback’ effect is achieved by enabling therapists to identify clients at risk of treatment failure so that therapists can pay greater attention to client difficulties, which may be hindering therapeutic work. To date, little attention has been given to understanding relevant mechanisms of formal feedback in psychological therapy. In order to understand and maximize the benefits of feedback, it is essential to explore potential mechanisms contributing to this effect. Research in social psychology may help to explain how feedback works. Methods Findings on cognitive biases in the field of social psychology are explored and linked to preliminary findings in the field of psychotherapy research. Results Research on cognitive biases and expertise is congruent with indications that clinical prediction in psychotherapy is unreliable and that it may be difficult for clinicians to detect errors in their judgement as a result of a lack of clear corrective feedback. This problem is linked to the fact that clinical outcomes occur in a complex ‘noisy’ environment where prediction is inherently difficult. Conclusion Formal feedback may derive its benefits from its ability to help correct naturally occurring biases in therapists' assessment of their work. If these biases are seen as normal, but often avoidable if feedback is used, this may pave the way to greater acceptance of formal feedback by clinicians and enhanced outcomes for clients. Copyright © 2014 John Wiley & Sons, Ltd. Key Practitioner Message The use of formal feedback tools can help therapists overcome inevitable limitations in their ability to predict poor response to treatment, enhancing the likelihood of detecting and resolving client difficulties in therapy.