Sometimes I feel the same way, when I try playing pieces that I really love. I feel as though every time I play I make a mistkae and it doesn't sound right. I guess it's a question of precision?
Now, I need to warn you, all of you who are frustrated about your "shortcomings" and your mistakes.
DON'T FOCUS ON YOUR MISTAKES WHILE YOU PRACTICE!!!
I have written about this many times before, and I will write it again, and again, because this is so important. I practiced like that for decades - or rather, I practiced less and less because it was no fun. I was whipping myself mentally with all my mistakes. I heard nothing but mistakes. I was furious with myself - why can't I play anything right? So I build up all those negative feelings ... I wanted so badly sit at the piano and play all this wonderful music I loved, and all I heard was an idiot at the keys. Better to find a good recording, then? Yeah. And that is how an active pianist ruins the joy of her own playing and returns to the passenger's seat.
There a millions and millions of ex-pianists in this world, and many of them still love to listen at piano music ...
Then I made a 180 degree turn in my thinking and now I make progress like never before. Why? Because I decided to throw all my "goals" away and focus entirely on my PROGRESS. After each practice session - it may be ten minutes or 90 - I ask myself "so, what did I improve now?" I can always find something. It could be some really stupid little thing, but I always find something. I make myself happy with the thought of the things I just learned.
Mistakes? Are just perfections I have not yet learned. I'll learn them too. Stay tuned, I have found some very useful tricks lately.
This seems to be a negligble thing, but I assure it is not. You got to focus on you progress and your achievements. You got to simply ignore your mistakes. The result? You will always leave your piano in a happy mood, as a winner, and be eager to return and keep on practicing. And your mistakes will vanish ... well, everybody makes mistakes from time to time, even the best ones, so don't be upset about them. I have heard the most wonderful and perfect performances, where there pianist made several mistakes, and nobody gave a d*mn. Most of the audience didn't even notice.
But OK - let's say you always make the same stupid mistake every time, or almost every time you play a certain piece. This is a bit dangerous, because every time you make the same mistake, you will program it even harder in your muscle memory. You will keep on making this mistake, getting more and more angry with yourself, and this will affect your whole interpretation of the piece. So, you have to get rid of it.
Worst method, which I unfortunately used for years: play the same part over and over again, hoping that the mistake will vanish by itself, if you only play fast enough - like trying to get over a hurdle by running faster and faster against it ...
Try this one instead:
https://practisingthepiano.com/?p=2610That is, make a deliberate STOP right before the note that you always get wrong. Deliberate and planned. Play in tempo - STOP - gather your thoughts, plan your next move, place your fingers right, keep on playing ... And yes, you can have this stop even in the middle of a long run. Do this again and again, and your stops will become shorter and shorter and eventually you have programmed yourself to play right,
without hitting the wrong key.
Of course you need to analyze your mistakes thoroughly first. Take your time, find out exactly what you are doing wrong. Just repeating the difficult section over and over again, with no further analyzing or mindful thinking, is stupid.
And so the usual tips, of course: play a lot with hands separated, even when you "can" play with both hands. Play very slowly sometimes. Play sometimes so slowly that nobody can tell what piece you are practicing.
Do a lot of mental playing while you are not at the piano. Read the sheet, imagine yourself playing the music, really imagine your movements. And just hum and sing the piece to yourself, make it your "second nature". You should feel it with your whole body. (I am a bad singer myself, so I don't sing aloud, just in my head.)
It is also helpful to record yourself a lot and analyze what your hear afterwards - unfortunately it is not always what we want to hear, because it is very revealing, but it is of good help.