What is Self-Discipline

Have a powerful reason — when things get difficult, “because it sounds nice” or “to look good” aren’t going to cut it.
Start tiny, with a simple but unbreakable promise to yourself to do one small thing every single day.
Watch your urges, and learn not to act on childish whims.
Listen to your self-rationalizations, and don’t believe their lying ways.
Enjoy the habit, or you won’t stay with it longer than a week’s worth of sunrises.

Self discipline means that the only one that you are accountable to is you.  That does not necessarily mean that you can do anything you want.  It means you have an internal set of standards which you feel that you, not necessarily everybody else, must
live up to.  That doesn’t mean that this set of standards is exclusively yours and/or goes against God’s set of standards.  You are, however, accountable to you when it comes to these things.  After all, who is the most effected if you don’t live up to these standards?  You are.
Not having self-discipline often means that a person believes that they can wiggle out of having to do something because somebody else  is making them do it and they don’t know what they are talking about and/or sometimes you just have got to do what you want to do, not what everybody else wants you to do.  Scarey isn’t it?  You have to determine whether you are doing right or wrong.  You don’t have to necessarily convince anybody else that it is the right thing to do or that it is not the wrong thing to do.

Responsibility is the most important part of the equation when it comes to self-discipline.  Going to confession and being told what penances you should do to pay for the sins you have committed lets you “off the hook” so to speak and you think you don’t have to do anything else.  Self-inspection or reflection is an important part of the process of self-discipline.
Self discipline is developing a set of standards to live by that is constantly being revised as one’s understanding of life grows and changes.  I can change me, but not necessarily you, and that is the most important thing.  If I believe in something strong enough, then I will live that way no matter what other people do.