Showing up every day is one of the most important lessons I've learned. It applies to almost everything – learning or improving a skill, fitness, solving a problem, or anything in between. In many ways, it riffs off of many different facts and ideas:
The power of compound interest. Small amounts become large amounts when compounded daily. Most people overestimate what they can do in a year and underestimate what they can do in ten years.
Practice is essential. Showing up every day forces us to practice. It lets us try new things without pressure (if we fail, we can try again the next day). When the time comes for the performance, we've built muscle memory through practice. And sometimes we discover quality through quantity.
Habits work. Showing up every day is one of the best ways to create habits. See Don't Break the Chain and other daily activities.