I had a therapist a while ago that spent a lot of time talking with me about how discipline and motivation aren't real. His point was that lots of people lose before they start by feeling like they aren't disciplined or motivated people inherently. And ultimately, the only way to measure motivation or discipline is to measure something else - "I was motivated to stay fit because I went to the gym"
He also spent a lot of time with me on understanding that motivation and discipline are most times just thin wrappers around what people actually want. Thinking less about "If I were just more disciplined I would be able to do this" and more about "If I actually wanted to do this I probably would", and then focusing on what you actually want, or why you don't want something, is probably a much more valuable of a use of time for some people than thinking about motivation or discipline.
I am not posting this to say "If you're a disciplined person, you're wrong" - but moreso "If you're a person that believes you struggle with motivation/discipline, maybe you can rethink those concepts".