But honestly, I think what holds most of us back is a better ability to just don't do that. Take that thing you want to make, and instead of planning out all the pieces, just make the tiniest possible thing that could possibly be of value. Using this example, just start with "Today" and the 4 buttons. Make a thing that shows your 4 buttons of exercise you will click on each day. You can probably make that today. No streaks or freezes or calendar view. Those are all great ideas, and you'll get to them. But you need momentum. And you'll probably decide you don't even like that calendar view in a few days. I think more projects need a kick in the pants of just do something small. Get it done today. See what the next task is from that point because it's probably not what you thought it ought to be during the planning phase.
This also isn't exactly easy either. It requires some thought and discipline and find the smallest thing and commit to shipping it without distraction. But it's also something good to practice at.