Discipline is important in every aspect of life. It allows one to have power and control in life, and play a part in becoming successful. A disciplined person expresses their skills through Perseverance, Tenacity, self-control and resistance to temptations and distractions.
Discipline enables one manage time properly and in day to day life even during practices and exercise. Arriving on time is discipline, explaining to the instructors about the injuries one has is discipline since it avoids problems during your practice.
With discipline one is able to act accordingly, aligning with thoughts, rather than feelings. A disciplined person plans their lives and works hard to reach their goals. Exercise and lots of body fitness balances the mental capability by learning how to accept failures and setbacks.
One is able to sacrifice instant gratifications in favor of long term goals.
Discipline works best when it is self-imposed rather than forced, Yoga teaches us to love and respect ones opinion no matter the outcome.