Hi,
I have been playing piano more than 9 years. I am what you may call amateur because I studied another career.
Despite playing for 9 years, I feel sometimes that I have many gaps in my technique, that I haven't dominate the basic.
I returned to play the Hanon lessons, I am with Bach's Inventions 1, 4, 7 and sooner with the 8th one. I am learning Chopin's Prelude "Raindrops" and another piece from book 3 of Thompson's.
In theory, I know by heart the scales, the key signatures, the clefs, and how to transcribe from one instrument to another.
Why do I feel that it is not enough?, what is considered to be the basic principles on playing piano?