Self-control

Self-control is the ability to regulate one's emotions, thoughts, and behaviour in the face of temptations and impulses. It is an aspect of inhibitory control and classified as an executive function since it is a cognitive process that is necessary for regulating one's behaviour in order to achieve specific goals. However, the lack of self-control or excessive self-control both extremes are deleterious to one's mental health. 

On the one hand we have individuals who are into substance abuse who are characterised by their desire for instant gratification in other words their lack of self-control to delay reward. They show greater temporal discounting due to their impulsivity which leads to their addiction to narcotics, gambling, shopping, overeating, pornography etc. 

On the other hand we have individuals with Obsessive Compulsive Personality Disorder (OCPD) - a mental health condition that causes an extensive preoccupation with perfectionism, organization and control over self and their circumstances. These behaviours and thought patterns severely interfere with maintaining positive relationships with others.

OCPD is an impairing disorder chiefly characterized by their excessive capacity to delay reward.  Individuals with OCPD show less temporal discounting due to their excessive self-control which along with their desire for perfectionism leads to their difficulty to complete tasks and experience internal reward related to goal accomplishment. 

Thus, the ability to exert self-control lies on a continuum in which one extreme is impulsivity (leading to addictions) and the other extreme is excessive self-control (leading to OCPD) - both extremes are associated with mental health problems.

Reference:

1. Pinto, A., Steinglass, J.E., Greene, A.L., Weber, E.U. and Simpson, H.B., 2014. Capacity to delay reward differentiates obsessive-compulsive disorder and obsessive-compulsive personality disorder. Biological psychiatry, 75(8), pp.653-659.
   https://www.sciencedirect.com/science/article/pii/S0006322313008287