My pastor has a definition of discipline: Remembering what you want and what you don't want. It's not exactly Webster's but it seems to work especially when talking about "self" discipline. If a person remembers what he wants and remembers what he does not want then it seems he will make choices in life based upon those remembrances.
Let's take an example: A person wants to be healthy and fit and does not want to be a flabby, unfit couch potato. This person then will make choices which will lead to a healthy, fit body and avoid choices which are counter productive to that end. Simple, right?
When the alarm goes off at 5:45 A.M. screaming at me to get up and go to the pool I often toy with the idea of staying in bed. But then I remember what I want and I also remember what I don't want. Morning swimming has become a habit, which also is an important element of self discipline. When you have a good habit you don't have to think about whether you are going to do it or not...you just do it, and don't permit your "self" to argue with yourself. It is easier to keep a good habit going than to restart a good habit that's been broken.
Some say it takes 21 days to form a habit. It all depends on if you really know what you want and remember what you don't want. Go for it!