Musical genius can partly be described as the ability to sight read. Sight reading is the musical art of playing music one has never heard or seen. There are many stories of the legendary abilities of the great composers. Mozart was said to be able to read and play any music instantly. No practicing, no rehearsing.
Mozart could write out the four separate parts of a string quartet before he had written out the complete score. This means that he had a perfect mental impression of every note in a piece he had never played, and never heard.
Unimaginable Facility Of Beethoven
Beethoven once had to play one of his piano concertos on a piano that was a half step out of tune. With no time to tune the instrument, there was only one choice: play the concerto not in the key of C, but in the key of B, a monumental technical feat. No problem, said Ludwig, and did it straightaway.
This is like you are about to play Hamlet. Just before you go on, the director demands, "Do it in Swedish." But Ludwig spoke every musical language there was.
Liszt Could Read Any Music Instantly
Liszt was legendary for his technical flights of fancy. Once the composer Grieg brought the great master his A minor piano concerto, which he humbly showed to Liszt in a handwritten manuscript. It was a very messy manuscript. By Grieg's own account it was full of scratched out passages and terrible music handwriting.
Liszt calmly opened it, looked at it for a moment and then played it perfectly, and with gusto in front of the dumbfounded composer. All the while Liszt missed not a note. He kept up an erudite and witty commentary on the orchestra parts. These he played as well, along with the solo piano part.
Liszt Knew Every Piece Ever Composed
Liszt is said to have played every known piece in history, perfectly, in his weekly master classes. And this included not only piano music, but any music, operas, symphonies, concertos, popular music. Anything. In a spirit of encouragement, remember that even Liszt had to develop this breathtaking musical craft.
When he first came to Paris as a teen aged firebrand, he was a gawky 16 year old Hungarian boy. He needed to acquire polish in order to become the first genuine superstar of classical music. Now go back and practice.