With regard to frustration while training...after many years of training, I have learned a very useful technique: the blank look. Feeling frustrated is bad enough already, it doesn't help to spread that feeling round the dojo (or "share the pain" as a friend of mine would say). So when I get frustrated because I'm having trouble with techniques, or when someone helpfully tells me something that I don't agree with or knew already, or when a higher grade demonstrates a technique to me so many times that I don't get a chance to practice it...I practice THE BLANK LOOK!
But seriously, frustrations pass. The best we can do is to just keep trying. Sometimes when I'm feeling that I'm stuffing everything up, I try to focus on one (just one at a time) of the general principles: I'll think about being centred, extending ki, keeping my hands soft but with meaning, being relaxed but ready, unbendable arm, large circles - small circles...there's plenty more...it seems to help to disengage from the particulars of what I'm trying to do and think generally. If it doesn't actually improve my technique immediately, it t least stops me from dwelling on how frustrated I feel and how crap I am