What's hard, though, are things like actually moving to the next step. Are you even practicing correctly, continually pushing yourself to new heights, or are you defaulting to the riffs or melodies that you like to play because they're easier?
The hardest part for me, currently, is trying to learn music theory on my own. I've tried getting into the creative side, writing songs and melodies, but so far, that process isn't very fun at all because of my lack of knowledge in scales, chords, and progressions.