Some of the songs I've written were too hard for me to play. Not joking - I knew what needed to go where but couldn't hack the riff.
What to do I wondered? I'd try replacing the hard piece with something similar but easier to play. Right...Does the term 'bitch' seem appropriate here? And of course I'd play it slowed down and practice it a lot.
I realized about a year ago that this was actually a blessing. My normal practice starts with some wild licks with lots of triplets and so on to get the blood flowing in my fingers (and give that pinkie a workout - lazy finger)
Next thing then is work on the songs with a part I haven't mastered yet or alternately one that is still in progress. Sometimes use a cover piece to learn a technique as well. It's become a helpful practice because I'm forced to practice things outside my comfort zone.
Another thing I do is relearn my own songs playing a second guitar part - typically I don't write for rhythm or lead - like Planet was saying, I'm going for the music. However - I leaned or should say, relearned, the need for the songs to have a strong, intelligible rhythm / chord version so the other guys can hear the changes.
Then there is the 'dead zone.' Symptoms: one does not enjoy playing much and seems to have no creativity; rhythm can be impacted and one feels just sort jaded in an uncool way. Kind of like 'writer's block' I suppose except writers don't do exercises on their keyboard to stay nimble.
I try to push through those times since they usually seem to lead to a new plateau - I end up sort of measurably better just because I kept the muscles moving in my fingers while my brain digested what it needed to do.
Another trick that works for me against the 'dead zone' is to switch to a different guitar. A tele is good for that because it is so measurably different in feel and sound than most other guitars. For some unknown reason that works better than switching over to bass.
I sometimes feel like I'm satisfied with my playing but it doesn't last.
I doubt I'll ever 'master' music - neither songwriting nor playing. I typically feel like I'm a pretty sorry player. Sometimes I envy the guys with the huge egos.
Talbot