The first question should be: to what level am I expected to perform? If you are playing only for your own personal enjoyment (and you are not a zealous perfectionist), then it would be ok, as it is in my case, to play through a composition with a few mistakes and slips. Or even rubato because that's the way you feel like playing. However, if you have to perform a piece for exams or a recital, then of course the mindset is completely different. I have trouble staying focused. I hear recordings of compositions played by better players on this site, and it makes me want to have a go at the piece. However, I have to restrain myself because I know that I am not that good and couldn't even get passed the first five notes. What I have found that works FOR ME, is to find a composition that really blows my socks off and is not too terribly difficult. If during the course of the stuttering through the piece I find myself hating it, I just toss it aside. If you have no external pressures (i.e. exams, recitals), then there should be no pressure to complete a piece you are struggling through or hating every moment of. That's the good thing about music for the self, it is for your own pleasure and you can do what you want to do! I hope my ramblings help. -JG p.s. If not, then you can always hire a person to stand behind you and every mistake you make they will hit you over the upper back with a small stick of bamboo and shout: "NO! AGAIN! WRONG!"