I was always the type to start something and not finish it. I lose interest. There was a brief time in my life where I had this realization that all I was doing was literally eating, sleeping, and shitting. I didn't get, "angry," but I got motivated. I decided the thing to do was pick one thing, just ONE, thing, and see it through till it's end.
I decided to learn the C programming language... I also took a few college courses around that time, and I didn't have enough time to finish what I had started, so, I set it aside; but, I returned and finished it. I suppose I am now an amateur C programmer. That was many years ago. The next thing I decided to learn was HTML/CSS. I did finish that, too. Then honeysuckle happened, things got better, more honeysuckle happened, things got worse again, etc...
I don't think it was about discipline, actually, as I am not a disciplined person. During that time, it was about motivation. I knew that my interest and passion for programming wouldn't amount to anything, it wouldn't help pay the bills; but, very simply, I had decided to start ONE thing and see it through till it's end. So, I don't think it was even about the programming, it was about picking ONE thing and finishing it. They say to pick, "realistic," goals, so you don't keep overshooting and missing your mark; but, at that time, I had chosen one of the hardest programming languages to learn. Hat off to my stuborness. I'm glad I did it, though. I proved I could do it, and, ultimately, that seemed to be most of what it was really about. I enjoyed the HELL out of those two learning experiences, it was great. Most people probably learn C in a computer science class in college and of those people, probably 70-80% hate the class and material; they just have to do it. I enjoyed it. Wonderful time of my life. I am constantly wishing I could get back into that passionate high and thrilling enjoyment of autodidactic adventures.
It seems to be a great mystery of life. People want to quit smoking. People want to find a better job. People want to work less. People want to be their own bosses. People want to follow their passion and ditch their shitty job; but, most don't. Most dream about it, go to work, and settle for chinese take-out. I suppose my motivation back then had an element of discipline to it; but, I was motivated, plain and simple. I wasn't pushing or hauling dead weight. I had a destination gas in the tank to get there. The trick is, is there isn't a self-help book in the world or a map to be found on how to get that sort of motivation. I think you can search for it for years and never find it; and, other times, it can pop up in a matter of days; or, even hit you on the head when you weren't even looking for it.
It's sort of like when you are trying to remember an actors name; but, you just can't reach it. You can see their face. You can remember the scenes they were in; but, in the midst of your conversation with some one, you just can't pull the name out of your head; and, for all the trying harder of it to do so, you will probably drift farther away from the memory you are seeking to retrieve. Or, like, a puzzle, when you get stuck and can't find a piece. Anywho.
I know the circumstances that brought me to such motivation and I know the circumstances that lead me away from it; and, neither were really anything I did, all that intentionally. Good fortune came, and good fortune went. The motivation hit me on the head. I had all the right ingredients for it and bam, I realized I could make a tasty dish. Then, the famine came...
I could be wrong; but, I think discipline is useful for doing the things you don't want to do; which, can later help you be able to do the things you do want to do, perhaps. I think motivation is another thing entirely. If I'm motivated to learn French to a level of fluency, and I can maintain that motivation, it will happen. Discipline won't be necessary, so much. However, if I need to learn calculus to get my degree; but, I hate math and suck at it; I think discipline is the best bet to getting through that, if it's possible at all.
Though, I doubt anyone who has achieved anything notable has always been motivated. Maybe some; but, probably not most. I don't know, maybe they are one in the same...