Each musician has her own signature sound, touch, interpretation, so that you can tell who is playing a piece when you hear it, even if you don't know beforehand who will be playing. When you hear Isaac Stern, you know it's Isaac Stern. When you hear Itzak Pearlman, you know it's Itzak Pearlman. When you hear Liberace, when you hear Mancini, when you hear Harry Connick, Jr, when you hear Alasdair Frazer, you know who it is! Each musician artist has his or her own signature sound and touch of their instrument and interpretation of their music. Each artist musician has his own "voice" in his/her instrument! The instrument becomes his/her own "voice", just as real as a singing voice!
It's not just any ole person playing the instrument. It's not that just anyone can press down the keys of a piano, can press down the stops of a flute, or pull the strings of a harp, or pull a bow over the strings of a violin. It's not just the scientific, mechanical motion of "playing" the instrument. It involves an interpretation and energy that comes through the artist, comes from the heart and mind and soul, to interpret the music and produce a beautiful sound. This is where the true art comes alive and it's more than what you can get from books or lessons or printed music. It's the Soul of the music that's interpreted by each individual artist.
This is why it's not just the 'piano' that you're hearing. It's that artist's piano. It's MY piano. It's not "the piano", as if all pianos sound alike. It's MY piano. It's MY harp. It's Carol's harp. It's Dayna's violin. Each one sounds different than someone else playing a piano, harp or violin.
This is the true art of playing music: when a musician can interpret and play beautifully from the heart, not just pluck out the notes from a piece of paper. We all have our own unique sound, even tho we're all reading from the same sheet of music.