Almost 50 years ago I was changing strings on my first ever guitar and trying to tune up a string. Problem was, I later realised, that I was aiming at an octave above what the string should be.
Unsurprisingly, the string snaped with some force and the end of the string embedded itself into my forehead right between the eyes.
From that day to this, I’ve never changed strings without slipping a pair of glasses on.