Took me about 3 years until I finally could say to myself "Hey, i'm half decent". There's a learning curve for everyone and it's a good thing to doubt your abilities in my opinion, makes you work much harder (at least that is the case with me).
If you're working very hard it'll all pay off in time and you'll be glad you stuck with it. I remember spending pretty much all of last year playing furiously and getting nowhere and sometime around septemberish there was this one day when it all just came together and it was an absolutely amazing feeling. Hope that helped.
Whether you're a newbie at playing guitar or playing it for quite some time, I think the best way is to practice all of the time or if you had free time... Just don't give up, you are going to learn it in time, just don't stop practicing and make sure you are practicing correctly, or if you have some resource person it would be great if s/he is with you while you're practicing...
I remember when I was still new at learning how to play guitar, i thought it was impossible to learn the tricks that experts can. But as I play it often, without even realizing or knowing it, I could say I can play at least much better than when I was starting and I realized that no matter how impossible for you to get the skill at first, by practicing and putting some passion for it, everything is possible.