Discipline is what makes a leader stand out from the crowd. A person who will scorn or excuse self discipline will never qualify for leadership of a high order. The very basic of leadership principles start with character. Successful people are willing to do things that unsuccessful people will not do. John Maxwell talks about the difference between character driven and emotion driven people. Emotion driven people make decisions based on how they feel, convenience, attitude, what is easier, popular, and quit when problems arise.
Character driven people do the right thing regardless of how they feel, are commitment driven vs. convenience driven, make principle based decision vs. what is popular, action is controlled by attitude vs. attitude controlling the action, ask what are my responsibilities vs. what are my rights, continue when problems arise, quit when problems arise, steady vs. moody and a leader vs. a follower.
Discipline is the mark of maturity. Without discipline the character will remain weak and juvenile.