The Practice Hours Count
This article says it all.
The number of hours spent on a piece of music matters. It’s quite discouraging how slow, painful and frustrating to get a 4-bar section of a tune sound good. But one must practice it, play it making all the mistakes possible until no mistakes remain.
There’s one caveat though: In particular playing guitar, bad playing can become ingrained in one’s playing. Thus one must practice very slowly to get it right using proper techniques.
Slow and long hours of practice will prove success, no matter how hard the tune.