kind of a revelation to me, the dominant 7th chord. For the longest time, I didn't play or even particularly like playing this chord. It didn't have the fat creaminess of a regular root fifth root M/m third bar chord. As I've been recording more and more, playing straight barre chords got kind of bland. Trying to improvise over them really didn't have much variety.
Then somebody posted a video talking about 7th chords and it gave me an idea. I tracked progressions with 7th chords, then I tracked leads along with it. A light bulb went off. I was getting more notes that fit in with the chords and the leads were, for lack of a better word, more lively.
As someone who wanted to get right into the screaming notes of Ritchie Blackmore's SOTW when I started taking lessons and my teacher was trying to show me "Greensleeves" and "Girl From Ipanema", I didn't really learn theory from the ground up. I learned a bunch of patterns and parroted them endlessly, but didn't really 'say' anything at least in my opinion.
I've been teaching myself more and more theory in the last few years and it is finally starting to make sense. After I mess around with this for a while, I'm going to start working on 9th chords.