There’s this old saying in cycling… “It never gets easier, you just get faster.” That’s really not directly comparable here… But maybe there’s something to it. 
For me, I guess theory and harmony came pretty quickly to me. I remember in 2000 or so stumbling across the website Guitar Wars, where members would post compositions and be randomly matched against each other and the community would vote on which they preferred - sort of silly, and it could have been REALLY shitty, but the overall feel was good natured camradere and about giving good constructive feedback and seeing your internet buddies gradually get better at playing and recording. And, one common refrain early on, for me, was that while I was a pretty decent player, especially for my age (19 or so at the time) the fact that I was occasionally including harmonized melody lines that were both key-appropriate, but also generally not just straight parallel harmony, was sort of unusual for a guy who at that time had only four or five years of playing under his belt. The supreme irony, of course, was that I generally DON’T like the sound of harmonized guitar, and that I was definitely way more blues based and way less neoclassical in my writing. I do still enjoy putting supporting harmonies way back in the mix under chorus melody lines, and stuff like that, the kind of detail in a composition that you definitely have to look for and that doesn’t really call attention to itself. I’ve always found finding little interlocking parts to support a song a lot of fun.
