Discipline, or mortification, is when you work really hard to control your thoughts, feelings, and actions. It's like when you want to eat a lot of candy but you remind yourself that too much sugar is bad for you and you shouldn't do it. It means making choices that might be hard or uncomfortable at first, but will help you become a better person in the long run.
For example, if you want to become really good at playing an instrument, you need to practice every day even if you don't feel like it. That's because if you practice a little bit every day, you will get better and better over time. It may seem hard to do at first, but after a while it becomes easier and more natural.
Another example is when you have to study for an important test instead of playing video games or watching TV. It may not be as fun in the moment, but it will help you learn and remember important information for the future.
Overall, discipline means doing what you know is best for yourself even when it's hard or uncomfortable. It takes practice, patience, and effort, but it is an important part of becoming a responsible, successful, and happy person.