Going back to the late 80's/early 90's I was into neo classical metal - Yngwie and the like. The band I was in played mostly originals, but we did so covers. One of the covers was an Yngwie song called Krakatoa. It is a truly difficult song- very fast runs doubling the guitars (yngwie played the bass on it, and it shows- like him or not the man is a technical monster). I worked and worked at it, and at times could play it if I was absolutely playing at peak capacity. It really drive me nuts, and probably was one of the leading causes of me obsessing with flat out speed, which lead to me developing tendonitis in my left wrist/forearm.
If I had been smart I would have just admitted to myself that it was just a bit beyond what I could do, and just told the guys in the band that I cannot do it. It would have saved me a bunch of discomfort and down time recuperating (think not being able to play for about a year), and then for another year or so only being able to play for 20-30 minutes. Ok now though.