system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If repetition strengthens our synaptic connections, what happens when we over-practice, and seemingly start to get worse?

Practicing an instrument for example.

You are learning a part. The more you repeat, the better you get. But if you overdo it, you start to get worse the more you play. So you put the instrument down and come back 1 or 2 days later and you find that you can play the part better than ever before. 

What is happening here?
gpt
Fatigue, for one part. Maybe others can chime in on the neurological aspects of learning, but you can't forget that playing an instrument is a physical activity and if you practice for a really long time, you get tired.

It's similar to exercise - once you've done several sprints, you won't be able to do more at the same level without some rest. It works the same way for music, there's only so much your muscles can do and you will need to rest at some point.