He couldn't see a thing. How did Jeff become such a good guitar player? I have a hard time looking away from the frets without screwing up. Even if he played the guitar flat and was sliding he would have to count them all out. Just knowing where they are all at in the heat of the moment would be impossible.
Muscle memory probably. The same way you can play chords without spending ages getting your fingering (lol) right he probably memorised exactly where his frets were.
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It's not as impossible as you think. Upright bass, violins, violas, etc don't have frets, your fingers just have to get used to where to go to play the notes you want to play. Play guitar long enough, and you'll find you can play tunes you are really familiar on with your eyes closed.
Like others have said muscle memory. Most decent guitarists can play without looking for at least part of the time.
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I play in the pitch-black dark sometimes to practice being able to do that. It's actually pretty useful, especially if you're going to be playing out at smaller venues. They often seem to have terrible lighting and sometimes even dim their already-poor lighting. At least that's my experience
Practice, practice, practice. Then do some more. Remember when you first learned the main riff from Smells Like Teen Spirit (I assume you did, as did every other budding guitarist)? I bet you can play that without looking at the fretboard. The same applies to more complex stuff the better you get.
The more you play, the better you get at knowing where the frets are. It's like being able to type without looking at a keyboard with enough practice. When I was playing seriously, I could play my band's solos and riffs without looking. Just enough practice. He could probably associate where his fingers/hand was on the fretboard with a specific note or chord.
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