Being positive should never be about closing your eyes to tragedy or injustice. Bad things are going to happen in the world. But someone with a positive attitude will be able to look beyond the tragedy to the next step. Positivity finds solutions where others only see problems.
One way you can develop more discipline is to use challenges. This makes it more like a game and less like a chore. Also, there can be the element of competition with others, and having others help hold you accountable improves your odds of success.
Challenges are very popular and you can find them in many places. Or you can make up your own and share it with a group of people. You also can make your own challenge or use one from someone else to just challenge yourself. However, you end up doing it is up to you.
Discipline is not always easy, but it is well worth it. When you set goals and work on them every day until you accomplish the goal, you feel proud of yourself. Not only because you accomplished the goal, but because you did not quit.