The #1 issue for people addicted to playing their guitar. If you play classical then its not so bad (nylon strings are much kinder than metal), but for everyone else learning to play guitar means wearing down your fingertips until they're hard and painful. Sexy, no? Thankfully this doesnt last forever. Once youve basically filed away your fingerprints youre set with hard skin on your fingers for life (which also has the benefit of setting you up for a career in crime without the need for gloves). Even then, a mammoth session can leave your fingers sad and indented for hours afterwards, but as they say - no pain, no gain.