A Profound Statement, Made by a Great Musician...

I once asked a great pianist what, for him, was the most difficult piece he had ever worked upon.
I expected something like "Islamey" of Balakirev, or, the infamous piano reduction of the third movement of Tchaikowsky's 6th Symphony.
What I got was a rather unexpected answer, and within a fraction of a second after my question was asked. Without blinking, he replied "nothing is easy."
A deep discussion ensued about the elemental requirements endemic to any piece of great music; that is, what to be done with the notes having been learned - in other words, the creating of music.
The traditional, or should I state the most popular reaction, is to be dazzled by the pyrotechnical attainment of a piece that requires a great physical technique, such as a virtuosic performance of the Liszt Sonata by a Horowitz, or a Richter or a Gilels. There is, of course, the normal awe of the listener when a piece of great physicality can be conquered with the seemingly relative ease that the great virtuoso can demonstrate.
But to give as much musical power of meaning to, say, the "Arietta" by Grieg, or "Chopin" by Schumann or the "E" minor Prelude of Chopin, each of these one page in length, resulting in a reaction just as awe-inspiring as one receives upon hearing the Brobdingnagian difficulties in the Schumann Toccata is the true test of what a great musician faces and recognizes.
And this is what this great pianist meant in his answer to me; namely, the reality that about twenty percent of the time in the learning of a piece of music is to put the notes into place, and about eighty percent of the time remaining is to decide about what to do with these notes.
For those of us not in the genius category, we can only, with a degree of envy, try to picture that delectable reality.