I have experienced several failed attempts at learning to play guitar, each resulting in a few year layoff in frustration. I can't play lead. I can't shred. But then one day a buddy of mine came over and just started chugging away at some cool rhythms and it was like the heavens opened up on me.
Since then I've made more progress in three months than I had previosly made in years. I've fooled around with chords, scales, attempts at shredding and stuff, but it all ended in frustration. Now, for some reason the guitar makes sense to me. Rhythm guitar. Look at Malcolm Young, he rules and the guy never takes a lead break.
Tunes and progressions are just spilling out of me now from just one short bit of inspiration. I'm glad I didn't give up again.
Just a bit of inspiration for anyone frustrated with their progress. I kept a guitar in hand for ten years, more or less and never got much better until now. Do it because you love it and don't worry about the rest, it'll come.