Despite the popularity of the Ancient Greek maxim 'know thyself', the importance of self-insight for adjustment, or effective psychological functioning, remains unclear. Here we examined four perspectives about how cognitive and emotional abilities and self-views about these abilities relate to adjustment. We administered tests of cognitive and emotional abilities and assessed self-views about these abilities. Participants then completed daily diaries for a week to report multiple self-reported indicators of adjustment. We analysed data using polynomial regression and response surface analysis. We found no support for benefits of self-insight. The conditions to infer support for linear or curvilinear associations between abilities or self-views about these abilities and adjustment were also not met. The findings suggest that giving employees and students feedback about their cognitive and emotional abilities in organizations and in schools may not enhance their adjustment. We discuss the limitations of our study and offer suggestions for future research. PROTOCOL REGISTRATION: The stage 1 protocol for this Registered Report was accepted in principle on 21 June 2018. The protocol, as accepted by the journal, can be found at https://doi.org/10.6084/m9.figshare.c.4283567.v1 .