As we read the last two verses of 1 Corinthians 9 we see the power of choice. We choose whether we are disciplined or not disciplined. The concept of "I can't help it' is often untrue. The purpose of building a disciplined life is to be at our best to love others. Ultimately love is sacrifice for another best. Many of us are not wired to be regimented. We are contrarian or creative. Living disciplined life will help us.
Know your bent
I find people have three bends to them: short, mid, or long term ability to be disciplined. We really need all of those types. We often choose not to be disciplined because we look at long tremors and get overwhelmed. Purpose of discipline is to be at YOUR best. A big part of that is learning how you're wired. If you're a short termer, focus on short one or two week spirts. Never mind. Focus on one weeks. If you're fairly disciplined but see yourself fall short, focus on 2-3 months goals and nail them. Discipline is a means to the end of being an amazingly loving person.
The purpose of challenging yourself in things that don't matter is it trains you to handle hard situations that truly do matter. Stretch and grow yourself. One of the keys to living longer is to stay active in growing your mind. That and friendships do far more for your long term life. While we age our capacities may not be as great, but that does not mean our ambition to be the best us possible has to.
Know your mission
What drove Paul's disciplined life was his mission to reach people for God. Each one of us has a part in that mission, though it will look different to each of us. God already has a Paul. He needs the best you. Articulate why God has you hear on earth. Do that. It is hard to be disciplined for disciplines sake.
So, get moving! I believe in you!