Only recently, the question whether within-person personality variability is a blessing or a curse for job performance has reached the agendas of industrial and organizational (I-O) psychology researchers. Yet, this limited stream of research resulted in inconsistent findings, and only little understanding exists about the role of rater source and mean-level personality in this relationship. Broadly following socioanalytic theory, the present study examined the extent to which self- and other-rated within-person personality variability predicts self- and other-rated job performance, and whether this is moderated by mean-level personality. Within-person personality variability indices and job performance evaluations were obtained from an experience sampling study including N = 166 teachers, N = 95 supervisors, and N = 69 classes (including 1,354 students). Results showed that-above and beyond the effects of mean-level personality-self-rated within-person variability was positively associated with self-rated job performance, while other-rated within-person variability was negatively associated with other-ratings of performance. Many interactions with mean-level personality were found, mainly demonstrating negative effects of variability for those with a less adaptive personality profile (cf. variability as a "curse"), while showing positive effects of variability for those with a more adaptive trait profile (cf. variability as a "blessing"). Importantly, however, additional analyses provided little evidence for associations across type of rater source. These findings contribute to the field of I-O psychology by highlighting that perceptions of within-person personality variability may impact performance evaluations beyond personality traits, although its desirability seems to depend on individuals' personality trait level. Implications and limitations are discussed. (PsycInfo Database Record (c) 2023 APA, all rights reserved).