There are quite a few Korean noun options for the word "discipline" (징계, 훈련, 학과, 기율, 억제), and I am trying to figure out which word(s) are most appropriate for conveying the virtue of self-discipline (and not "discipline" in the sense of "punishment" or "academic field"). For example, if I wished to tell someone who eats too much junk food or watches TV instead of studying that they need to have more "discipline", what word(s) would be most appropriate?
If you had to say 'you lack self-discipline' or 'you need to be more disciplined about it,' that might be:
너는 자제력이 부족해. (You have an insufficient degree of the power of self-control.)
너는 자제력을 좀 길러야 해. (You need to increase/nurture the power of self-control a bit.)
Or 'this is a matter of discipline' (meaning 'self-discipline') might be:
이건 자제력의 문제야. (This is a matter of the power of self-control).
However, you lose much background by translating in this case. Discipline is what a 'disciple' undergoes. When the disciple misbehaves there may be a 'disciplinary' committee. After years of that, the student may now have 'self-discipline' and can behave in a 'disciplined' manner, and so on. Thus, to an English speaker 'discipline' may figure as an obvious ingredient of success along with such things as 'motivation' and 'opportunity.'
A concept more natural to a Korean speaker may be effort, or 노력. If someone gives up on a program of exercise or study, the comment may be:
너는 노력이 부족해. (You lack effort--or are not trying hard enough.)
If the (given up) thing had to be put up with rather than pursued, the comment may go to patience.
너는 참을성이 부족해. (You lack patience.)
I realize these don't work very well for binge eating or TV (which does not obviously require effort or patience). These, I believe, a Korean speaker is likely to connect to some pursuit, e.g. losing weight or studying. Then the binge behavior can be re-cast as lack of effort or patience in that pursuit.
If the Korean speaker does say '자제력,' it may sound more fresh or original than a reference to 'discipline' in English.
I think 절제 is the word you are looking for. You can say "사람이 절제 할 줄도 알아야지."