This is something I tried to instill in my children from a young age, and I think I succeeded although it didn't appear so at the time.
Self discipline extends to so many areas of life.
The discipline to apply yourself to a task, be it study, work or housework, the discipline to say 'no', to do what you say you're going to do, to give back to the community, to exercise judgement on how and when to spend to improve your life and when to restrain yourself...it's all the same skill.
The ability to tackle a distasteful task, to uphold a promise, to do what's 'right' not what's 'comfortable', to manage your life and your money in a manner that recognises that delaying gratification actually means that you can enjoy the REALLY good things in life, rather than just the ordinary ones...it all comes down to self discipline.
I think all of us have a little child and a parent in our heads. The child goes 'ooo...I really want that new iPhone/new car/kitchen appliance...it's so cool and everyone else has one so I deserve one too'....and the parent goes 'no, you have an iPhone/car/kitchen appliance and it works perfectly well, and this is a want, not a need'. This internal conversation might go on for some time, be it seconds, minutes or months.
Eventually though, one will win out over the other. Sometimes our inner child wins, and that's okay occasionally. But it's when our inner Parent starts to win out more often, that we really see our lives leap ahead in ways we may not have expected.
Suddenly that overseas holiday (not paid for by credit card!) is a reality, that investment property is in our reach, and having money available for emergencies is something we don't even have to think about.
Exercising self-discipline is like exercising our body. It's hard at first and takes a great deal of conscious effort. But in time, the more often we say no to our Inner Child and listen to our Internal Parent, the easier it becomes.
Who will win your internal debate today...Child or Parent?