The biggest thing to understand is that it wouldn’t be normal if this didn’t happen. 🙂 The way that I explain it is that you will have one bad day for every two good days playing the violin. So 1/3 of the time you will feel like you can’t get anything done, and you are not playing as well as you know you can. This still happens to me after playing for 26 years. I just hope that it doesn’t happen on a day when I have to perform. As you get more advanced, I would say your standards get higher and your mistakes will become less noticeable to the average ear. But you will never avoid the two steps forward one step backwards philosophy. If you keep moving forward though, you will always make progress!
One tip is to not look at progress day-to-day or even week-to-week. The best thing you can do to truly rate yourself is to look back 3-6 months to see how you have improved. Do you feel you are a lot better today compared to then? Does the piece that was very hard for you to play then a lot easier now? That is what you should always do, and looking anything short-term can be dangerous. 🙂
Do you guys out there feel you are a lot better now compared to 3-6 months ago? Share your thoughts!