There was a time when my left hand fingertips turned green due to a chemical reaction from normal body oils to the guitar strings. It was during my Doctoral years, when I was preparing a concert, which, in hindsight, should have been split into two programs. It consisted of all challenging pieces: Bach’s Fourth Lute Suite, the Ginastera Sonata, Sor’s Grand Solo, Albeniz’s Mallorca, Sevilla, Torre Bermeja, and Tango, the Ponce Suite, and Rodrigo’s Invocation and Dance. I was practicing daily and through the night.
One day, I noticed that there was a small split on my first finger. My teacher kept having me go over the opening of Sevilla, where you have a half-bar going to a full bar while bringing out the middle voice clearly. I remember practicing that opening passage over and over again until, on the day of my concert, the bar would get caught on the split on my finger, which had now grown bigger in only one day. This led to the cancellation of my concert. That evening, I had four stitches put on my index finger. I remember it did not hurt and it did not bleed, either. I was practicing again soon as if nothing had happened.
But this taught me a big lesson about the importance of programing. You don’t need to play all the pieces that you know in one concert. Teachers should dissuade students from doing that, however ambitious they are. In my case, I was lucky it did not lead to a more serious injury.