system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does muscle memory work? Why do we get better at something through repetition?

One of the interesting things I remember from learning musical instruments is when you're really trying to play some musical piece without any mistakes, you try multiple times, then sleep it over, and on the next day you'll be much more skilful at playing this.  
  
Back then, it seemed to me like a some sort of magic. So, if I went through time and met a ~~12~~ 5-year old me, how should I explain how muscle memory works?
gpt
There are lots of nerves in your brain, which can connect to each other in lots of ways.

When you do something - like tying shoe laces, playing an instrument, walking, or driving - you cause some of the involved nerves to form connexions with each other.

The more you do this, the stronger these paths become, reinforcing the action by making the "signal" that the nerves give in this situation stronger.

Eventually, the signal from this nerve pathway will be so strong that you'll do it 'automatically' without going through your "upper-brain" (consciousness).

This process is commonly called the "1,000 hours" automaticity, though the actual amount of time doing something to cause this to develop varies depending on task, the individual and the action involved.