You may think that developing discipline is about limitations. This thought has probably been reinforced by previous attempts at changing your bad habits. Actually, it can be very empowering to develop discipline. Think back to when you managed to make a change in behavior that was successful, how did you feel? When you overcome obstacles in your path, and accomplish something with consistent work, you feel like you can do anything.
When you are not self-disciplined, you often do not accomplish your goals and feel like you are not worthwhile. You tend to put yourself down more and in general have a more negative outlook on life. You may set yourself up for health issues, in particular those related to obesity, or have trouble in your relationships with friends and family.
Successful people do not get there just because of luck. They make goals, plan how to achieve them, and then develop the discipline to accomplish those goals and plans. They do fail, they do have obstacles, they may even modify the goals or go in a different direction based on working on those original plans.
If you want to succeed, you need self-discipline. You may want to get rid of bad habits like smoking, gambling, and overeating. You may want to form good habits such as exercising, reducing clutter, reading more books, watching less television, or saving money. You can accomplish these habit changes if you focus on one or two at a time, and consistently act on those goals over time. One is best, though if you are trying to lose weight, you may find it better to combine dietary changes with exercise.
The biggest obstacle to discipline is not lack of willpower, but a desire for instant gratification. Especially in modern society, everything seems to be focused on having things done quickly. People eat instant oatmeal or cold cereal instead of having a cooked breakfast. You grab a burger at a fast food restaurant instead of bringing a healthy lunch to work. Television commercials tell you that you can have this or that right now, if you pay by credit card. The problem with that of course is the interest you later have to pay on those purchases.
You can improve things where you are not in debt, are healthy and fit, and have stable relationships, but it will require giving up instant gratification, and adopting self discipline. It will not always be easy, but you will find it quite empowering to achieve your goals for a better life.