After years of playing traditional tunes on mandolin, some melodies stand out for me as being especially hard to master. These tunes usually don't SOUND any more difficult to play than the rest of my 60 tune repertoire. And since very few of the tunes I learn are played in scales outside of the usual D, G, C, A, F, Gm, and Em) its not a question of having to wrap my fingers and my brain around an A-flat scale (for one example).
Plus, some of the tunes that have actually been quite easy to master, can sound like they'd actually be hard to play, maybe because of some exotic-sounding accidental note, or maybe a sudden, fast legato movement. La Bastringue comes to mind. Or how about the outstanding B-part melody in Rights of Man. Before I learned Ragtime Anny, I was sure that the opening rat-a-tat sequence would freeze my fingers. It's proven to be as easy as pie at full speed. Yet I have a much harder time playing the similar rat-a-tat sequence in Bill Cheatham. I don't know why.
Trying to figure out precisely why some tunes remain so indefinably difficult, all I can say, is that in many cases the fingering sequence seems to go against the "grain" of what I am used to expecting. Well maybe that's not always true, since I am now learning some Chopin and Bach, and I am finding that these pieces are not any more difficult to play than anything traditional. Because these classics are usually longer in duration, they do take an "ear learner" more brain cells to play well all the way through.
Anyway, I'd be very interested to hear what tunes other traditional mandolin players are having a hard time with. If you decide to respond, it would also be helpful to let us know how many tunes you can actually play at full speed, just to give your personal struggle a real world context.
My own hardest tune these days seems to be Colored Aristocracy. I can play it OK in my own living room, but that's not at full speed. When I crank up the speed at a dance, there's two different places in the tune where my fingers always go into a rut. Then I have to start THINKING about finger-brain coordination right in the middle of the tune, which is a dangerous mindgame for any melody player standing up on stage.