Here's my two cents, for what it's worth... I too, have been playing for many years now and because I love the way it sounds when it's right, I push myself to make it sound more and more pleasing. Your frustration is a sign that you also care about that outcome and that's good too. Sometimes I have to just put the guitar down for a day or two because I can't get a particular run or solo. Then when I pick it back up, things fall into place better and my perspective changes again! You know if guitar was easy, everybody would be playing. It's probably why they made games like guitar hero because everyone wants to be one, but that road is narrow and not everyone can put the time and effort to get there.