Studies have shown that some people can mentally isolate stressors so that they do not affect performance in other areas. This is sometimes referred to as isolating or repressing the memory of the stressor so that it does not influence secondary reactions. The recollection of the memory is just as painful as it would be for anyone else, but the memory itself remains isolated, and thus there is no opportunity for the memory to form associative links with other memories, where it could thereby affect self-esteem, sense of achievement, or productivity. 
There have been numerous studies that support this idea of isolation. First is the notion that this effect is not observed in those who demonstrate high neuroticism, or difficulty controlling affective discipline. Studies have shown that people suffering from depression will respond to damaging thoughts by thinking about other negative thoughts, thus reinforcing the depression.  In contrast, those who demonstrate low neuroticism and high defensiveness were more likely to process negative feedback in a minimal fashion , thus "isolating" the negative feedback from the self. In addition, they were more likely to minimize relative impact by spontaneously generating positive thoughts afterwards.
This is an important notion, as the role of emotional regulation and achievement is readily apparent. Studies have shown that emotional regulation in school children can predict teacher-student relationships, academic achievement, and productivity . Furthermore, positive emotions, moreso than negative emotions, appear to be associated with heightened attention and thought-action repertoires. 
Thus, it may be the case that with increased self-discipline comes an increased ability to inhibit (or 'isolate') negative emotions and stressors. This can be mediated by executive functioning tactics such as inhibition, or by shifting cognitive focus (particularly onto the task at hand).  Executive functioning abilities are largely mediated by the frontal lobes and by the prefrontal cortex. However, the ability to 'isolate' stressors in order to maximize productivity and motivation may be more closely related to neuroticism, which is in turn related to reduced connectivity between the left amygdala and anterior cingulate cortex, as well as reduced cardiovascular activity. 
 Hansen, R. D.; Hansen, C. H. (1988). "Repression of emotionally tagged memories: The architecture of less complex emotions.". Journal of Personality and Social Psychology 55: 811–818.
 Schul, Y; Schiff, M. (1995). "On the costs and benefits of ignorance: How performance satisfaction is affected by knowing the standard prior to performance". Personality and Social Psychology Bulletin 21: 491–501.
 Edwards, J. A.; Weary, G. (1993). "Depression and the impression-forming continuum: Piecemeal processing despite the availability of category information.". Journal of Personality and Social Psychology 64: 636–645.
 Bonanno, G. A.; Davis, P. J.; Singer, J. L.; Schwartz, G. E. (1991). "The repressor personality and avoidant information processing: A dichotic listening study.". Journal of Research in Personality 62: 386–401.
 Graziano, P. A., Reavis, R. D., Keane, S. P., & Calkins, S. D. (2007). The role of emotion regulation in children's early academic success. Journal of school psychology, 45(1), 3-19.
 Fredrickson, B. L., & Branigan, C. (2005). Positive emotions broaden the scope of attention and thought‐action repertoires. Cognition & emotion, 19(3), 313-332.
 Wegner, Daniel M.; Schneider, David J.; Carter, Samuel R. & White, Teri L. (1987). "Paradoxical effects of thought suppression". Journal of Personality and Social Psychology 53 (1): 5–13.
 J. Ormel, A. Bastiaansen, H. Riese, E.H. Bos, M. Servaas, M. Ellenbogen, J.G. Rosmalen, A. Aleman. (2013) The biological and psychological basis of neuroticism: Current status and future directions. Neurosci. Biobehav. pp. 59–72