I couldn't agree more. I gain a great deal of fulfillment from the study of music. In essence the study of playing a musical instrument is also the study of self-control. It requires a massive amount of patience, hard work, and discipline to play a musical instrument well. It's amazingly difficult to get your fingers to do what you want them to do. You have to learn what your hands can and can't do well and learn to work with them. Everyone is different. It takes time. It take REPETITION.
This is important. Suzuki mentions it several times in his book. The power of repetition can not be underestimated when it comes to playing a musical instrument. Here's a personal example. Whenever, I perform or go to jams where I improvise a lot I find myself falling back into these familiar patterns of playing. I've practiced other licks, songs, and passages but I can't seem to play them out. Why? It's simple really. I've haven't practiced them enough. The songs and licks I play best are the ones I've played the longest. The ones I've played the most times.
Now that might seem like a no brainer but it's important to remember this when practicing. If I hope to get these new musical ideas and songs into my fingers I have to play them that much more. Repetition. I can't expect to practice a song once or twice a week and expect to play it up to speed. It needs to be constantly nurtured and worked on. Muscle memory take time to develop.
If you find yourself frustrated with your playing remember the power of repetition. Focus yourself on one small problem and keep working on it till it improves. How long will that take? Hard to say. But I can tell you with absolute certainty that you will see results if you start small. If you're working on a song. Play the first 1/2 of that song 100 times and see how much better you are at it afterward. Play it 200 times. Experiment and see how long it takes to see improvement.
Devote yourself to one song for a month and see how well you play the song at the end of the month. Let me know how it goes.
Hope it helps.