One thing all great musicians do is to constantly aim to get better. The same is true with most things in life, but the correlation is most easily true when compared to athletes. This is because of the physical nature of athletics. Playing an instrument is similar. You have to build muscles and coordination in your fingers and hands on a stringed instrument. Golfers are always working on and perfecting their swing. Baseball players and tennis players the same thing. Swimmers on their stroke. Etc.
When first starting out on a stringed instrument, most likely your fingers wouldn’t do what your brain told them to do. You had to build up strength and coordination. If you were playing 3 finger style banjo, you might slowly work on one roll until it felt natural. As you progress you might start to focus on precise timing and tone of your rolls.
I’ve been playing 5 string banjo for over 30 years, and at a fairly advanced level. But recently I was noticing that when I played my rolls at certain tempo, my rolls would just get a bit choppy. I worked on the rolls with a metronome. I went back and played them slowly, focusing on getting very precise timing and tone. They got a little better, but still not where I wanted them.
As I was practicing some single string bebop lines, I noticed something. My middle finger of my right hand wasn’t playing each note with the same tone as the others. I then tried playing slowly some scales just with my middle finger of my right hand and found it very difficult to do cleanly with a good tone. Also, my finger got tired very quickly. When I tried the same scales with just my thumb or just my index finger I had no problem. Hence, I knew I had to work on my middle finger.
The same goes true when learning a new song. Many players will play the song from the beginning and somewhere in the middle, they hit a spot that gives them trouble. They then start at the beginning of the song and hit that trouble spot again. They do this over and over and get frustrated. Instead, when they find that trouble spot, they should start right there and focus on the hard part of the song. Eventually it will become easy. Again, focus on your weaknesses and fix them.
If you only continue to do what you’re good at - anywhere in life - you will not grow. Focus on what gives you trouble and work on it. Your playing will vastly improve and your frustration of not growing as a musician will go away.