Any given piece of music is going to have parts that are harder than others. Maybe you're having trouble with just a couple of short parts that you can't seem to get right. To play those parts you will have to improve. Can you? Or do you just keep running up against the wall. Sometimes the solution involves finding a missing piece. A new way of looking at playing the song. If you're stumbling over one or two parts (the hardest parts maybe) of a song run through this checklist.
- Are your fingerings the best they could be?
- Have looked at the problem in a new way?
- Everybody makes mistakes
Finding the missing piece is often a matter of persistence. You look at something for long enough and you'll start to see things you missed before. As the Jazz/Bluegrass banjo player Pat Cloud once told me at a workshop, "Practice trumps all."
Hope it helps.