Why must you have discipline?

Anything you want to accomplish in life requires having some form of knowelege/understanding/talent to some degree and perseverance to a larger degree. The only way in which you can face issues and keep the goals alive long enough to accomplish them is to persevere, and perseverance requires discipline . You need to be disciplined to take on the challenge of making a sustained effort over time, dealing with setbacks and also not getting stuck on small victories but moving on to the bigger ones that get you closer to accomplishing your goals.

Why have you answered your own question?

I doubt jobs and money are the only reason for discipline, though. Discipline helps you build character, which makes you more likable to friends and potential mates, as well.

Without discipline anybody will not grow yourself.