I had a room-mate at college who tried to get me riled by saying "when you can play "Anji" you can play guitar". I spent a whole term on it. In desperation, a friend lent me the music, which was "wrong" for the version I had on record, and in C#m because Davy Graham played it with a capo on the fourth fret. Two days after my room-mate and I went off on industrial assignments (not to see each other for six months), I got the hang of the dang thing! Then again - I can do Anji, Wildwood Flower and Classical Gas at the drop of a hat these days, and quite a lot of other things, but two tunes that I've always found extremely hard are "Stagefright" by Dave Evans and "Singing in the Country" by Rick Schoenberg. It's not like trying to do a Doc Watson impersonation, where you can hear what's needed but just can't play it right now. With those two tunes there's so much going on, my tiny mind just can't take it in!