Get a second opinion: Comment on Bleidorn et al. (2019).

Bleidorn et al. (2019) argued that personality traits, as important determinants of life outcomes, should be the object of treatment interventions. They suggested that self-reports on standard personality questionnaires provide necessary and sufficient evidence of trait change. However, the self-concept-on which self-reports are based-may change without any alteration in the underlying trait. Additional evidence, such as that provided by independent informant ratings, is needed, and multimethod assessments should be a feature of all studies of trait change. (PsycInfo Database Record (c) 2020 APA, all rights reserved).