I agree with 3donkey about the hours and hours on one thing. You're not trying to be a robot!

If you eventually go back to something you couldn't quite master and it sounds better then you thought it might you might get a pleasant surprise and finish off what you couldn't do before.

Play with feel and don't worry about the times you sounded like crap, this happens to everybody. Move on then come back on yourself now and again and realise how much progress you've made.

Good luck!