I'm getting better at handling my frustration...So far as I can tell my main source of frustration is I'm trying to go too fast. Either I'm literally trying to play a section too fast, just beyond my speed threshold for that passage even... Even though everything else will be at the right tempo, when I get to the hard part I try to play it as fast as possible. It's strange.Or, more likely I'm trying to learn the piece too quicky and haven't gone through it thoroughly before moving on, as a result the whole piece... falls to pieces and I get frustrated.So for me, the answer is usually to slow down... Be more patient.Looking back, it seems to be part of a larger cycle: When I get my routine down pat and get learning things very smoothly and rapidly I get the urge to take bigger and bigger bites, before long every bite I take is more than I can chew and I choke myself.Try playing through with a metronome to check for how evenly you're playing (if you're speeding up certain spots and not knowing it)... Slower than what you're aiming for, up to what your aiming for and even a little faster than what you want... Maybe it's just certain sections stumping ya and you've just gotta iron those spots out.