Self discipline, in the common sense is a device for empowering the ego. But properly directed self discipline can deconstruct the self and lead to ultimate freedom.
What's mostly thought of as self discipline is making the self do something we think we outta do, or not do something we thing we shouldn't do. These are delusional attitudes that give mental conditioning more control over our lives.
The ability to self discipline is an important key to Freedom through realizing the Truth of who we are, but self discipline is only valuable when its wielded in service to Spirit/God/The One.
Specifically, having the will and the intent, while emotionally triggered, to witness all forms of thought without following them, to remain present to the breath, and to feel unconditionally what's coming up is the ONLY form of self discipline that affects the cause of internal and external dis-ease.
This ability is developed through practicing stillness of mind - which means consistently taking time out of the busy lives we have created to do nothing 'productive' but watch our thoughts.
All of our behavior changes organically, in exactly the way it 'should', in response to awareness of Truth which comes through stillness - while every trip of disciplining the self to be a certain way is in and of itself resistance to the Truth we seek.